I received a machine from a customer that would not boot. The machine had been operating flawlessly for several months… then suddenly it would not boot. The typical error was: “The file is possibly corrupt. The file header checksum does not match the computed checksum. Also, once in a while I got an error from BOOTMGR:.  I ran diagnostics on both of the hard drives (mirrored) in the system from a BIOS diagnostic option and they reported NO errors. [more]

I could not boot from the Windows 7 CD. I could not boot from the recovery CD made from Windows 7. I finally made a bootable USB drive with DOS and it worked. I then saw an option in the BIOS to run a memory test… did it and it failed.

The entire problem (after hours of troubleshooting) was a bad memory stick!