A trojan or virus could gum up the works for Windows as well as boot sector viruses causing startup problems. Your friend most likely used the command line method of expanding a fresh copy of the bootmgr.exe file at the time in order to replace a corrupted or missing one.
The method generally advised like mentioned before for seeing that corrected with the Vista disk is seen at
http://www.howtogeek.com/howto/wind...ing-error-while-trying-to-boot-windows-vista/
The alternative method your friend used would be seen as rebuilding rather then referred to as expanding a replacement from a cab like seen in XP at the recovery console. That is also seen as Step #2 in another article on how to repair or rather rebuild the boot information(bootmgr.exe).
SOLUTION 2
If the previous method does not resolve the problem, you can rebuild the BCD store by using the Bootrec.exe tool in the Windows Recovery Environment. To do this, follow these steps:
- Get your Vista installation DVD and pop it into your drive.
- Then restart your computer.
- Press a key when you are prompted.
- Select a language, a time, a currency, and a keyboard or another input method, and then click Next
- Click Repair your computer
- Click the operating system that you want to repair, and then click Next
- In the System Recovery Options dialog box, click Command Prompt
- Type bootrec /rebuildbcd and then press ENTER
• If Bootrec runs successfully, it will present you with the installation path of a Windows directory. To add the entry to the BCD store, type Yes . A confirmation message appears that indicates the entry was added successfully.
• If Bootrec cannot locate any missing Windows installations, you must remove the BCD store, and then you must re-create it. To do this, type the following commands in the order shown below: (Remember to press ENTER after each command)
bcdedit /export C:\BCD_Backup
ren c:\boot\bcd bcd.old
bootrec /rebuildbcd
- Restart the computer.
http://cyberst0rm.blogspot.com/2007/04/how-to-fix-bootmgr-is-missing-in.html
Most trojans are better referred to as spies or downloaders that bring more crap onto the system while bootsector viruses tend to trash things like the bootmgr.exe seen in the newer Vista version of Windows. I suggest running a few full system scans with more then just one malware remover but a good antivirus program. A few sites like Symantec amd Trend Micros's House Call are better suited for that type of virus if present.