Unplug AC cord and wait 5min., reconnect AC cord, now try to power-up. What are the results? If still no boot, then you have a bad power supply or mtrbd. or both. The mtrbd. s"start ckt." lost its ability or blew. -OR- the power supply has blown. Usually the best to do is replace p/s and start from there. Replace with a higher wattage one if possible, it won't hurt the system to be more and better as the hi-wattage is room to grow on. Do this first before doing anything else, otherwise you may introduce other problems.
I was working as normal on my computer the other night. I have a compac computor with windows XP. It works great (until now). I decided to run a virus scan using AVG Free. It was late so I went to bed and let the scan run. Forgot to check it in the morning so i didn't check again until that evening. When I went back to my computer the sceen was black, I asummed it to be in sleep mode. I was not able to awake it. I shut it down and have restarted several times but I get nothing. It doesn't even try to boot up. Does anyone have a clue what might have happened?