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How to fix and prevent MBR (Master Boot Record) Virus or Boot Sector Virus

What is MBR viruses?

MBR (Master Boot Record) viruses penetrate the master boot code that runs automatically when the computer starts up. MBR viruses are activated when the BIOS activates the master boot code, before the operating system is loaded.

Viruses replace the MBR sector with their own code and move the original MBR to another location on disk. Once the virus is activated, it stays in memory and passes the execution to the original MBR so that startup appears to function normally. If you remove this type of viruses and if you’re not able to restore MBR, your computer become impossible to boot or start.

Some viruses do not relocate the MBR, just destroy the primary partitions listing in the partition table and your PC cannot start.

What is Boot Sector Viruses?

Many viruses rewrite the boot sector with their own code and move the original boot sector to another location on disk. Once the virus is activated, it stays in memory and passes the execution to the original boot sector so that startup appears normal.

How to remove MBR and Boot Sector Viruses?

Use well known commercial programs like Norton Anti-Virus software or you can download free Anti-Virus software programs like Avast! antivirus or AVG free edition by grisoft.com.

How to restore or fix MBR?

Read this post: How to fix MBR

How to prevent MBR and Boot Sector Viruses?

* Use Anti-Virus software, update latest virus definition and scan regularly.

* Set BIOS setting not to boot from removable disk, such as floppy drive, external drive, or usb flash memory stick.

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How to remove / uninstall GRUB loader or LILO boot manager.

If you have deleted all linux partitions and want to completely remove GRUB loader or LILO boot manager, and restore Windows 2000/XP OS MBR. (Master Boot Record)

Read this post: How to fix or recover MBR or follow the short instructions below.

1. Insert Windows 2000/XP Setup or Installation CD
2. Restart your computer
3. If you see this message, “Press any key to boot from CD…” press a key to start the computer from Windows CD.
4. After a few minutes, you’ll see Windows Setup Menu.  Press “R” key to start repair Windows XP installation using Recovery Console.
5. Microsoft Recovery Console will start.
6. If you’re prompted to enter a number related to the Windows XP installation that you need to repair.  Most likely “1″ if any.
7. Enter your Administrator password, if you’re asked.
8. At the Recovery Console Command Prompt, type “fixmbr” and verify that you want to proceed.
9. Remove Windows 2000/XP Setup CD from CDROM.
10. Type “exit” to restart your computer.

If you still have same problem, repeat the steps above but type “fixboot” instead of “fixmbr” command.

If “fixmbr” and “fixboot’ didn’t fix the problem, please read this post: Recover Hard Disk Data & Files.

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How to recover deleted, crashed Hard Drive Data & Files.

This post applies to Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Vista, Linux, and Mac OS X. If you’ve got “Error Loading OS”, “Error Loading Operating System”, damaged MBR, non-bootable Hard Disk, lost partition, and lost your data & files due to crashed Hard disk. You can recover your MBR, partitions, and recover your data by using right software.

Software you need:

Testdisk by CGsecurity.org
Download Testdisk here.

What is Testdisk?

Testdisk, created by Christophe Grenier is a extremely powerful free data recovery software! It was primarily designed to help recover lost partitions and/or make non-booting disks bootable again when these symptoms are caused by faulty software, certain types of viruses or human error (such as accidentally deleting your Partition Table). Partition table recovery using TestDisk is really easy. You can even recover your compact flash and other memory sticks.

Testdisk is available for DOS/Windows 9X, Windows NT/2000/XP/Vista, Linux, and Mac OS X

How to use this tool?

Follow this wiki TestDisk documentation carefully or you can follow the instructions that appear when you execute the Testdisk.

Instructions and screenshots:

Note: Before you proceed, please read “Fix Error Loading OS” post for your reference.

If you have installed Operating System on a single drive and you don’t have access to other computer to mount your damaged hard drive, you can download Ultimate Boot CD that contains Testdisk software. Visit Ultimateboocd.com

After you finish, you must restart your computer twice to see the results. At first restart, your computer will try to install your new (your recovered hard disk). On second restart, your computer will check your hard disk for any errors and try to fix everything before it loads operating system and hard disk data. If you have more than 2 hard disk drive, your partition disk letter can be changed.

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How To Repair MBR or restore Windows XP Master Boot Record

“Error Loading OS”, “Error Loading Operating System” or “MBR corrupt” on blank screen.

Note: Before you proceed, please read my other post “Fix Error Loading OS” for your reference.

1. Insert Windows 2000/XP Setup or Installation CD
2. Restart your Computer



3. If you see this message, “Press any key to boot from CD…” press a key to start the computer from Windows CD.



4. After a few minutes, you’ll see Windows Setup Menu.  Press “R” key to start repair Windows XP installation using Recovery Console.
5. Microsoft Recovery Console will start.
6. If you’re prompted to enter a number related to the Windows XP installation that you need to repair.  Most likely “1″ if any.
7. Enter your Administrator password, if you’re asked.



8. At the Recovery Console Command Prompt, type “fixmbr” and verify that you want to proceed.
9. Remove Windows 2000/XP Setup CD from CDROM.
10. Type “exit” to restart your computer.

If you still have same problem, repeat the steps above but type “fixboot” instead of “fixmbr” command.

If “fixmbr” and “fixboot’ didn’t fix the problem, please read this post: Recover Hard Disk Data & Files.

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How to fix “Error Loading OS”, “Error Loading Operating System” Windows XP, Windows 2000 error.

This is the error message:

“Error Loading OS”, “Error Loading Operating System” or “MBR corrupt” on blank screen.

You start your computer and you get nothing but “Error Loading OS” in white lettering on black screen. If you’re experiencing this error, your computer become unbootable. It looks like a catastrophic disaster and scary but Don’t panic. This can be fixed easily, if you diagnose correctly and follow right steps to correct the error. 99% of the time, you don’t need to reinstall your Windows XP or Windows 2000 operating system. Reinstalling your operating system is the last option. Most of the time, all of your valuable documents and files are still intact.

Don’t rush and jump into conclusion. You probably didn’t get the good results by searching the help and support site on Microsoft.com (I didn’t get the right answer when I had this problem)

Let’s fix this mysterious error.

Why do I get “Error Loading OS” error?

There are many different possibilities that can cause this error but I’d like to list them into 5 major groups:

1. Incorrect BIOS setting.
2. Your computer hard disk’s master boot record (MBR) is damaged.
3. Dual-boot issues with Linux or other operating system.
4. Overclock gone bad.
5. Partition or hard disk issues in new installation of Windows XP.

Verify your BIOS setting:

Access the BIOS by press “Delete” key or other key (usually F2 or Delete) specified by your manufacturer while starting your PC. Set correct BIOS setting according to your manufacturer’s manual.

1. Double check your system BIOS setting.
2. Double check your boot sequence.
3. Double check your disk option.
4. If you’re not sure, default setting will work for now.
5. Get the latest BIOS revision or motherboard updates from your manufacturer.

Restart your computer. If you still get “Error Loading OS” message, move on to next step.

What is MBR or Master Boot Record?

The BIOS reads and executes the first physical sector of the hard disk on the system. This first sector of the hard disk is called the master boot record, partition table or master boot block. There is a small program at the beginning of this sector of the hard disk. The partition information, or partition table, is stored at the end of this sector. This program uses the partition information to determine which partition is bootable and attempts to boot from it. It is the most important data structure on the hard disk.

Things you need to fix MBR:

1. Your Windows 2000/XP Setup or Installation CD
2. Administrator Password

How to fix MBR?

If you have single Operating System installed, read this full post: How To Fix MBR.

If “fixmbr” and “fixboot” didn’t fix your problem, Read this post: Recover Deleted Hard Drive Data & Files.

Hard Drive Data Recovery:

If you’re victim of MBR virus or boot sector virus, more likely your data & files are affected. Read this post: Recover Crashed Hard Drive Data & Files.

Dual-Boot Linux and Windows 2000/XP or other multiple operating system issues:

If you install Dual-Boot Linux with Windows OS or other multiple OS and uninstalled the Linux. You probably still have either GRUB loader or LILO as a Linux boot manager.

If you want to completely remove GRUB loader or LILO linux boot manager, read this full post: How to uninstall GRUB or LILO

If you want to repair damaged GRUB loader and LILO boot manager and continue to use Linux and Windows OS, read this post: Recover Crashed Hard Drive Data & Files. You will be able to recover your partition and boot manager to start your computer properly.

Overclock gone bad:

You probably installed Windows 2000/XP and tried to overclock your system. Your computer become unstable and you decided to change overclock setting and cause “Error Loading OS” error. You can restore your MBR. Read this post: How To Fix MBR.

Partition or hard disk issues in new installation of Windows XP

You’ve just installed Windows XP and restart your PC and get “Error Loading OS” error. This error is caused by your PC BIOS doesn’t correctly manage or support the capacity of the hard disk on which you are installing Windows XP.

To resolve this issue, use one of the following methods:

1. Install the lastest BIOS revision from your motherboard manufacturer or PC manufacturer.
2. Re-Partition your hard disk using latest utility software from your Hard Disk Manufacturer.
3. Install latest SP2 for your Windows XP operating system.

What cause MBR damage?

1. MBR virus or boot sector virus attack. Read this post: How to fix and prevent MBR Virus.
2. Power Surge.
3. Human error.

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