Optimax 3010 won't turn on

My apologies in advance if this has been covered before. This machine is probably 3 or 4 years old, and started shutting off by itself. Pushing the on button usually booted the computer up, but now I get nothing. There is an orange glowing light on the motherboard, and if I push the green button next to the power supply cord on the back, the fans run, the hardrive (I think) runs for a second and quits, the green light on the DVD drive flashes 5 times rapidly and goes out and the orange numbers "2" and "3" stay light on the front of the computer as long as the button is pushed.

There is nothing connected other than the monitor. I have removed the panel and unplugged and preplugged in many things, no help.

Any ideas? If I can get it to boot up, what can I check?