Computer not working

Clarifications

So if it's not blinking, I'm also assuming that you have already checked the ribbon and power cables connected to the hard drive(s)??

Are there any fans running?

Is there a lot of crap and junk Inside the case?

If so have you cleaned it out?

If you cleaned it out what did you use to do this?

Is this a new Power Supply that you fitted or one from another computer?

If it is from another computer was that one working before you pulled the Power Supply?

Have you made sure that all the cables are plugged in that you removed when you changed the Power Supply?
Have you checked the Data Cable fro the M'Board to the HDD?

Have you pulled the RAM and Video Video Card if there is one fitted and refitted them to this M'Board in the socket that they came out of?

What else have you done?

What where the symptom before this stopped working?

Col

First I'd make sure the PC Speaker is connected properly. The way your machine beeps or not at all could indicate what is wrong with it. If you get a beep check it out in your motherboards manual or online at the manufacturers site.

I'd try swapping out the ram and VGA card if you have access to spare ones.

If all that fails it's looking like mainboard. Before replacing it though clear teh bios by locating and switching the bios clear jumper. Do a search on google to find how to go about doing this on your board.