[For new readers: Yoki is my desktop computer. He has given me more than an acceptable level of grief lately.]
I took the drive out of the enclosure and plugged it in as an internal drive in Yoki. It works, and the circuit board looks normal too, so it is extremely likely that getting a new power supply will solve my problem.
Also got my new 1.5TB drive in the mail today. Put it in, and when trying to boot again, I get no video signal. I check the cables; they are secure. I reseat the video card; no change. I try plugging the monitor into the laptop as a second monitor; it gets signal. So there's nothing wrong with the screen or the signal cable. Yoki sounds like he's booting normally, but there's nothing on the screen, so.. did my video card break? How the heck do you diagnose something like that? Could I have bumped into it while wiggling the new drive into place?
..okay, got it working again, after removing the extra drive. That makes no sense. Why would adding a 1.5GB SATA drive cause the video card to stop working, when a 500GB drive does not? (Why would a adding a harddrive affect the video card at all?)
Removed the drive, reseated the video card a second time, and it works again. Put the drive back in, still works. Whew.
At least dealing with computer issues doesn't drain me nearly as much as other problems do.