I had two drives that would boot (Primary and Backup A), and one that would not (Backup B). Leaving Primary running in the laptop PC I normally use, I put Backup A into PC 2 and booted it. No problem. This is the laptop that we've assumed is working okay. I cloned Backup A to Backup B using PC 2. This means that neither A nor B had ever been inside the suspect PC on this go-around. The clone reported itself as complete and normal.
Neither drive would boot. I now have Primary cloning back into Backup A. We'll see in 90 minutes or so whether the clone of Backup A will boot inside PC 2.
All three hard drives (Primary/A/B) are 250GB Western Digital hard drives. Two were purchased at Fry's in Wilsonville OR, while the third came from Fry's Fremont CA.
Now that I've sort of tested the variable, I'm starting to wonder if my PC actually has the hardware problem (potential motherboard failure) we thought it might have. Maybe there is something wrong with the system installed on those three drives. The only way to test that would be to do a bare-metal WinXP installation -- something I'm almost willing to do, but not today. I don't have all day to spend playing with the computers. I'm working from home today (so I need at least one computer running without balking) and also packing for Westercon.
The current plan -- because I pretty much need to have at least one working laptop PC with me at Westercon -- is to make PC2 the working machine for now, and to have it booting from its own hard drive. I don't think PC2's drives have been contaminated with system files from PC1. I've also not put either of PC2's drives (primary and backup) into the suspect PC1 chassis. When I have time -- maybe next week after I get back from Tempe -- I will try doing a bare-metal installation of WinXP on one of the 250GB drives installed in PC1 and see whether it holds up.
Having five hard drives to keep two laptops running is not the happiest state of affairs. And there's still a higher chance than I like that I may end up completely offline while in Arizona, if whatever is troubling the trio of 250GB drives/PC1 starts showing up on the pair of 160GB drives/PC2. OTOH, neither of the 160GB drives has done a "will not boot" on me, so fingers crossed.