pci ide.sys corrupted and computer will not boot up

Hello everyone. It's been awhile but this was a big help the last time
i posted. I have a GRX-550 and a day after buying a backup 250GB
external HD, the computer stopped working. At first it would start and
say "Operating system not found";, but for whatever reason i could turn
the computer on and off and it would load up just fine. Now, it gives
me a message that the pciide.sys is corrupted and i can't even boot
from the recovery CD. Wouldn't let me into safe mode either. I hope
someone out there can help