I just spent 4 hours resurrecting an old Windows box now "grub loading. error"

[sassenach]

Grub is definitely a Linux boot loader. Windows prefers to be on Disk 0 and the boot partition should be active.

Try booting with your Win 7 disk and using the Repair facility, this should overwrite the mbr for you and create the 100mb hidden partition that 7 uses.

[codegreen]

Grub is the standard bootloader for most Linux distributions. It sounds like there was a Linux install on this machine at some point. The easiest fix is to boot to the Windows Recovery Console and use bootrec.exe /fixmbr