I built a desktop about a year ago that has, until a few weeks ago, been running without a hitch using Windows 7 Ultimate.

Recently, the PC started occasionally rebooting with a blue screen indicating a "PFN_LIST_CORRUPT" error. Also, I've seen at least once the error IRQ_NOT_LESS_OR_EQUAL.

I seem to remember temporarily connecting an internal DVD burner about the same time this happened. I burned a DVD for another machine and promptly removed the drive.

Yesterday, I reformatted the drive and installed Win7 Ultimate x64. During the first install, the PFN_LIST_CORRUPT bluescreen reared its ugly head again. A second install attempt completed with no errors. The fact that this error happened during a clean install leads me to believe that this is not a driver or OS issue.

I also ran the memory diagnostic from the Win7 32-bit install DVD. It completed both passes with no errors.

Periodically, the screen will flicker, as if explorer or the video are resetting. In the event log, I see a series of 8 or so errors indicating that some services unexpectedly stopped, and were apparently reset. These include an HID service and some others (I don't have a list in front of me).

The PC is a Phenom X2 3 Ghz with a 500GB Seagate drive, 4GB of Corsair XMS2 cm2x2048-6400c5c.

Anyone know what would suddenly cause a couple of sticks of RAM to go bad?