That was a nice indepth post, detailed to every aspect good alot of information.
Ok maybe I can help you out here, My older brother is a electrical engineer, I just happend to be on the phone with him now! He is saying that the red light on the UPS box probably means some type of power surge....................more than likely, caused by the idiot that came to your house! You need to go to the manufactures site or read the manual on what the red light means. Now my brother & I think it is your power supply tweaking out your video card or the particular Pci/AGP slot. I still need some more info on what type of work the guy was doing, plus the electrical layout of your whole house & some blue prints. But with that said, you can pretty much point the finger at that guy.......you can't prove it but hell, I would have a word with him.

Speaking of RadioShack ,here is the Toll-Free # for real uber tech support
!-800-THE-SHACK. I use it all the time, of course I'm into war-driving with my laptop. Every now or then, you will catch some of those guys," HAM junkies "who just came from the metro HAM fest & bought a nice piece of hard-line, try hooking up a BNC connector to that!