Progressive failure

My desktop seems to have died in a slow progression. Initially it was while playing Medal of Honor Airborne. The screen would go black and the keyboard and mouse lost function. I would have to hold the power button down to shut down. After reboot there was the "send error report to Microsoft" window. No other programs were affected, so I stop playing the game. The last week while on the internet it did the same, black screen & no mouse/keyboard. During reboot the "welcome to Windows" screen appeared and suddenly went black again. The power supply and case fans were working and the light that blinks while the hard drive works was doing its thing and the "On" button was lit. Holding the power button would shut down. Upon reboot, it wouldn’t reboot, but the fans were working. I waited a couple days and powered up. Everything seemed OK so I ran a virus scan and it black screened before the scan was completed. Thinking this may be a heat problem I cleaned out the dust from inside the chassis. I do this periodically, but did it again to make sure it was clean. A couple hours later I tried to start it up and got to my desktop only to have it stop functioning again. Yesterday I pulled the side cover off, checked all connectors and tried to power up. The power supply fan came on, while the chassis and processor fans started and stopped with the hard drive light steady on. Nothing else happened, and when I tried to hold the power button to shut down that failed. I could only shut it off by removing the power cable. Now when I press the power button on the power supply fan works, the hard drive light is on, but the "On" button has no light and does not shut down no matter how long I hold it. Neither chassis nor processor fans move. Looks like a trip to the repair shop. Any ideas would be greatly appreciated.

HP Media Center PC (m1180n)
Windows XP Media Edition SP2 (updates are current)
Motherboard Asus PTGDLA
3.4 GHz Pentium 4 550 (P) HT
1 GB memory
NVIDIA GeForce 8500 GT
250 GB SATA hard drive

 

It sounds very much like your power supply has gone south.

 

OK. The power supply was replace four months ago. According to the HP website checks, it's OK. The little green light is lit when plugged in and goes of shortly after unplugging. Does that sound right?