I've had my PC running fine for several months with XP. I installed Vista Ultimate 32bit yesterday and the install seemed to go well, Vista ran and looked good. I left for dinner, came home and it seemed to be in hibernation. When I woke it, two of my three monitors would not come up and I had to do a hard boot. Since then, the BIOS screen hangs after the beep and won't load.
Looks as though you might have hyad a bad install. Put in your Vista CD, and click on "repair"...at least this way you will not lose your files and it might load a little faster. Vista has the tendency to hang - or not load properly unless you are there to monitor its install...or so I have found with my PC.
Go into your Bios and set the boot priority so that your optical drive comes before the Hard Disc. You should be able to boot from the Vista disc then.
As for the root cause - The usual suspect is a bad device driver. If you can boot into Safe Mode, then you can look in the performance monitor (computer/advanced/perf...), check the errors, and get an idea of what happened.
If you get stuck and have to do a full reinstall, Vista will put your old data in a folder called "Windows_Old".