my compaq qill not power o. i just bought a brand ne antec 500 watt power supply! i recently had a keylogger on ym computer.....can it b sme type of virus on the computer that won't power it on?

Is there a light on your motherboard? If so, see if it's on when you power up. If it does, your power supply is fine and you might have to move on to other things. But if it does not come on, test the power supply and if it does not work, buy/find a new one and test if that one works.

i have new power pack and it worked for some time and tried booting the operating system but guess the hard disk is bad and i changde it but cannot power any longer

This has happened to my computer once before. Although there may be other reasons that can explain why your desktop isn't powering I would like to suggest that you try buying a new power supply for your computer. That may be the reason why it isn't powering on. If you aren't familiar with the inner components of your computer, I would recommend that you bring your computer to a dependable computer dealer or store that is reliable in troubleshooting/repairs, and pay them a fee to install a new power supply or even troubleshoot it for you. Good luck!