Dell OptiPlex GX150 won't boot.

[bkribbs]

Hey. I got a Dell OptiPlex GX150 a little while ago, and was told it worked, just there wasn't an OS. I tried to boot it, and it didn't. I left it until I had a chance to mess with it today. When I opened it, I saw a small solid yellow light on the mobo which is lit. What does that mean?

 

[bkribbs]

Ok, just in case someone finds this later on and needs help, a blinking light means the PSU is bad, and the solid means the mobo.