Re: Computer only starts when hot, otherwise it is a pain to turn on, . . .
I think setishock has it right. It is an intermittent problem, a hidden problem. As suggested strip the system down to a bare case and check for misplaced standoff to start with. Start with the basic system meaning mobo, CPU and memory (and video card if needed) to start up with. Take it from there by adding a component at a time.
It's pretty rare to have a bad solder or a break in the traces but I guess that's possible. The mobo would have to be badly mounted for that to show up. That's why I suggested starting with a bare case so you can catch it.
I yam what I yam