Self Test Check Your PC And Signal Cable...

[ashleygl]

If you don't even get a POST screen (white writing on a black background) your PSU would be the 1st suspect.

Yeah, that makes sense. Thank you. I just realized when unplugging those cables, that when I plug the power supply back in, it makes a really weird humming sound that I never heard before.

Is it hard to replace the PSU?

[Fed]

It's a simple task but if you don't feel confident you may be able to get a friend who can do it for you.
Do you know anyone who would lend you one to try before you purchase one?

[GX1_Man]

Usually only four screws once the case is opened and unplugging and replugging wires.

http://www.google.com/search?hl=en&q=how+to+change+power+supply

[ashleygl]

So I got a newer power supply (one that was in a computer that was barely used), figured out how to get it out. Took the power supply that I figured wasn't working in the problem computer... only to realize that the two power supplies are different so I can't even hook the other one up to the problem computer to try it. I put the power supply back in the problem computer for now, and it powers up so I didn't ruin it. Now I'm confident that when I get the right power supply I'll be able to switch them. It'll be a few days now before I can post an update to see if that will work. In the mean time, anyone else have any ideas?

[patio]

No further ideas are needed as you are on the right path...don't let them talk you into a cheap PSU...they're kind of an important part of a well running machine.

[Raptor]

Did you try swapping the videocard yet?

I'd reset the CMOS.

Just to get things straight: The PC does power on, right?

[ashleygl]

The PC powers on, but the only thing that shows up on the monitor is that Self Test Check Your... message.

[Raptor]

Reset the CMOS.