I was using the computer the other day and for some REASON it completely shut down on me. When i TRIED to switch it back on nothing HAPPENED.
The light is on inside but the power must be stopping somewhere as theres isnt as much the initial beeps when the computer switches on.
But any kind of hardware that requres the power of the tower to power up dont show the lights to say their working, (adsl, mouse, keyboard etc).
Im completely confused about this i cant see what the problem is, ive openend the computer and gave it a good clean so dust isnt a problem anymore so it should be working.
Its not the power lead ive tried 2 now, even changeing fuses but the internal light is on ANYWAY.

  Could do with some help on this on guys, all ideas are apreciated So you've tried two different power supplies with the same results?  Well, now it's time to narrow it down to other pieces of hardware.  What type of CPU do you have?  If it's a slot 1, make sure it's tightly secured.  Then I'd start by taking out all the necessary hardware you don't need in the system to make it run and see if it'll power up.  If it does, then one by one, start putting back in other pieces of hardware until you find the culprit.  

I've seen a BAD modem prevent a computer from powering up before so anything is possible.  Try and and let me know.  If you need additional help, you can contact me at ResourcePC.

DaveMore info on system............How old is it.......and what o/s make are you using.......maybe a hard drive failure!