OK, here's the latest.
The big computer with the problem, running off the 15 amp lamp circuit will maintain power up, but after 2 to 5 minutes the monitor says 'no video input.'
It's not the video card, I swapped out a brand new one, and same failure after 2-5 minutes...plus, I couldn't get the cd-rom drive to open after that same failure..
I'm flumoxed.
Why does the big computer work ok in the shop the last five times they've changed a part, and then it somehow fails here at home 10 minutes after I boot up?
Plus, the other computer is chugging along fine on the same circuit.
Here's my latest uneducated guess; no, wait, I cannot even guess.
Some kind of power surge got past the protector and damaged every part; and, as I swap out every part the next damaged element fails in 10 minutes or so?
Boot from hard drive...same problem.
Boot from CD with Win XP disk...same problem.
Swap vid cards same problem.
There's almost nothing left to swap. Fine, they say the same p4 chip now costs only $100, and a new hard disk might cost about the same. There is absolutely nothing else left from the old machine, besides those last 2 components, both less than 2 years old.
Too wierd.