It sounds very much like a hardware fault and apart from the few details you have posted.
Changed PSU from what to what?
Its an Asus mobo, which model?
You might as well add your GPU. Just to get a full picture.
You have now install Windows 7 on another drive, what type-size-has the problem occurred again?
Any error messages?
Do you get BSOD's if so what error codes?