I'm not sure if you're still having an issue with this, but that's a fairly common issue with PC's. It is something in your BIOS that is preventing the bootup process, as it is preventing the computer from performing its own Power On Self Test (POST).
So, when a computer doesn't post... you start from the most obvious, and unplug everything you don't absolutely NEED. So, unplug all USB plugs, and keyboard/mouse as well. See if it will start. If not, plug the keyboard and mouse (if PS2), and reboot.
If that doesn't help, then you're going to get your fingers dirty. Disconnect the power from the wall. Grab a small flashlight and, assuming this is a desktop, open up the side panel, find the little battery that looks like a watch battery, but bigger. Pry it out carefully. Look around the printed areas of the motherboard, and you should see a CMOS clear or reset button. It's usually a small black button about 3/16 of an inch. Hold down the reset button for about 5 seconds.
Reset, and reinstall the CMOS battery, and plug in only the keyboard and mouse. Then press the power button. As soon as you press the power button, look at your keyboard. The little lights (usually) at top of the Num Lock keys should light up momentarily, which should mean that the computer is registering that device (keyboard) as being connected.
If that still doesn't work... let me know and I'll PM you my phone number to offer you more help.
Good luck!
C:>