Vista - Bad power supply??

When I tried to boot up my 5 year old HP desktop XP PC a450n, it got about
half way through the boot cycle/sequence and everything in the tower went
dead. Pushing the power button does nothing and I've done everything in the
HP troubleshooting link below except disconnect internal connectors from the
power supply to the motherboard and back of all internal devices -- page 4
and then plugging it in. My PC doesn't have a LED on the back of the power
supply (as the instructions say) anyway so there would be no way to tell if
the power supply was getting power when I plugged it back into a wall
receptacle -- and the power button (diagonally across on the opposite corner
of the power supply) probably wouldn't work with the motherboard connector
disconnected anyway. However, I guess I might as well try that since
nothing else has worked -- right? I hadn't installed any hardware
recently -- this was just the first boot after a trip. Maybe the "jostling"
around during the trip did something? This is the first time I've ever had
this kind of problem. Do you know of any other way of checking the power
supply?

The power supply is 250W (not real large capacity) and I would probably have
to order a new one (assuming the old one is bad) from HP to insure it would
fit and have the right connectors, etc. -- right?

Click here: Troubleshooting Power Supply Issues

Thanks Gene