Not staying on

replace the switch

try to use screws

check the scrren inside the carb to see if it is ditry or needs replacing.

Which light is staying on constantly??

If it is the Hard Drive light - it could be because you plugged the cable to the hard drive in the wrong way around.

You will need to be more specific though.

What colour is the light? where is the light? any symbol next to the light? When does it stay on? etc

SPARK PLUGS FOULED OUT DUE TO LEAKING FUEL INJECTORS OR THE FUEL FILTER PARTIALLY CLOGGED.THAT WILL MAKE CAR HARD TO COLD START.

try taking a air hose and blowing all the dust out

may need carb clean or tune up

Not even beeping? Hard to tell from such little info. HDD doesn't work, CPU stays cold, that would indicate a motherboard problem, but then it would beep most of the times. It can be a a problem with your screen, but that doesn't add upp with the HDD, and the CPU staying cool (bye the way, how do you know that?)
I think you should take it to someone who can take a closer look on it.

First off, please use proper case. All upper case makes it look like you are shouting. Thanks.

Try removing everything you can possibly remove from the outside other than the monitor. Remove any cards inside not needed to boot (sound, NIC, modem, etc.).

Disconnect mouse and keyboard, too if it will boot without a keyboard. Some systems will halt at the BIOS screen without a keyboard.

When you have a minimum config for booting, boot and see if it stays on. If so, one of the items disconnected is the culprit.

If not, reconnect keyboard (if disconnected) and boot into Safe mode by tapping F8 after BIOS screen. See if it will stay on in safe mode. If it will stay on in safe mode, problem is O/S.

If it won't stay on in safe mode, see how long it will stay on at the BIOS screen. If it will stay on indefinitely, you could have flaky RAM or possibly hard drive. Power off, unplug power cable, remove hard drive and see if you can boot to the Windows CD. If it will boot up to Starting Windows and stay on, probably not RAM although that is not a definitive test. At that point, I'd try another hard drive and see if the O/S will install or try wiping and reloading the original hard drive.

Let me know if you need more help.

Honest1abe

The light is supposed to be on, it indicates 2 things

1) When it is being accessed
2) The amount of data on it. The ring glows more when it is getting full.