Windows won't boot, "nvata.sys missing or corrupt"

Hi everybody,
I'm running Windows XP SP3 on a homebuilt PC (ask me if you want the full configuration) and have been getting BSODs left and right, mostly of the KERNEL_DATA_INPAGE_ERROR variety. After getting a BSOD, my PC would hang in its initial boot process searching endlessly for the hard drive. I used to be able to fix this problem (temporarily) by resetting the CMOS using the reset jumper, but now that has stopped working as well.

Now when I try to boot, it recognizes my hard drive, but as soon as it tries to boot Windows, I get a black screen saying "nvata.sys is missing or corrupt." It recommends booting Windows using the setup CD and pressing "r" to enter the repair module, but doesn't offer any advice beyond that. I ran "chkdsk /r" and "fixmbr" but no luck. When I try to access the installation of Windows through the setup CD, it acts like Windows isn't even installed.

Can anybody help?