Okay so is the machine powered on, like lights on. fan spinning, but it won't POST? Or do you push the power buttong and nothing happens at all except for a clicking noise? Have you removed the side panel and looked if anything is blocking the CPU fan?
You can try the "paperclip trick" to see if the PSU is totally dead or not. Just google "psu paperclip trick". Just remember that it does not test the PSU under anything but a minimal load. However, if it does not work, the PSU is dead.