I forgot one thing. I have seen where the power switch can cause problems as well, so you might want to unhook the power switch where it connects at the mobo and simply use the flat end of a screwdriver and touch the 2 pins you just made bare when you unhooked the front power switch. If the switch is bad the pc will start. It does happen. These atx front power switches are not really even switches, all they do is cause a momentary surge of power, enough to cause the power supply to start itself up and then they are bypassed. However, if the switch is bad it will stick in the "on" position and cause the power supply not to start. So you can test to see if the pc will start with the flat screwdriver and if so then the front power switch has to be replaced. Its not common but it does happen. Happened to me once on a customers pc, took me forever to find the problem, lol. There are, of course, other things you can do, and there is one in particular i can think of, but from the sounds of the problem, i still believe its the power supply, so i would like to see you address that first, if possible.