Victor and mods, Since this does not really deal with the ubcd I hope I am not out of line by trying to help but it is not in me to not try...
Rstuff, you say the fans spin and the hard drive led comes on. Can you please answer the following?
1) OK, the drive busy light comes on but, if you listen close, can you hear the drive spin up? You may also be able to feel it.
2) Is your video card strong enough to need its own fan? If so is that fan spinning? If the fan is gone there may be a failsafe that shuts down the card to prevent thermal damage. If the fan does not spin it can often be easily replaced at a low cost. Just make sure that you get a fan that moves as much or more air.
3) You say that the drive busy light stays on for about a minute. That would sound close to a pretty good boot time. If you have your audio turned on do you get the Windows start up sound?
4) The system has been working for 'years', how many? This is an important aspect as, if it will be expensive to fix, you may be better off replacing.
As far as not having another video card around, if you go to a local shop you can probably pick up a used card from an upgraded system very cheap. If not I'm sure that you could get one one on Ebay for a few bucks. At this point you are not looking for a replacement for your card. You are just looking for a test board. If your current card is PCIe that does not mean that the test card needs to be also. If you have a PCI or AGP slot either would do to see if the system is boot-able. If another card works (with the current card removed) you can pretty safely assume that the current card is bad as long as it is not a fan issue. Well actually, if the test card is not in the same slot, the current slot being used could be bad.
Another option is to take the system to a local shop, stay away from the Geek Squad! They should not charge much just to test the video.
As to the ability for your power supply to start up your system I am not too concerned by what you report.