Thinkcentre S51 CD-DVD problem

[gb_ibmguy]

OK, I'm stumped.

My S51 (8171-2EU) just decided to stop recognizing it's DVD / CD rom drive.
Bios is most current version.
It had been working, it allowed me to install XP SP3 and all the Lenovo drivers etc. Not sure when it decided to go out to lunch but It seems to be related to latest windows patches. I've already swapped the drive with another known good one, swapped IDE cables, power connectors, XP restore points, reset to factory defaults, pulled the CMOS battery etc.
CD Drive light does not come on at all. Bios does not see the device and neither does Windows.

Strangely, this is the second S51 that I've had that has had the same exact problem. The first one I swapped out with the seller for this one. Never found out what the problem was.

System works, but, if (when) I ever need to reload the OS, I'm hosed. It's like the IDE channel is dead. The HD is a SATA and it works. No floppy in this system, so can't test that.

If anyone has any ideas, I'd love to hear them.