|Where did you get the information you posted in #2 above? The model number you posted indicates you have a Compaq Presario made by HP. It came with an Athlon 2.2Mhz processor. I am wondering where you are seeing the Celeron reference.|
Your computer came with Windows XP Media Center Edition pre-installed.
Where are you seeing the lights? On the back of the tower?
Are you sure you are unplugging the correct cord? Sounds like there must be some power going to the tower.
So when you try starting the computer you hear nothing and see nothing on your monitor, but you do see the lights on the rear?
Unplug again and then press the start button a few times. Plug back in and try starting it again.
Sounds like you might be in sleep mode.
Click on the link below to see your specs.