I start attempting to solve computer problems/situations...by eliminating possible causes. That allows me to focus on other possibilities, once I've eliminated the obvious.
I seldom know right away...what's wrong or why it's wrong.
The power supply is about as basic as a system gets.
FWIW: All those things you describe...could happen...and the power supply could still be at fault.
Worth reading, if not necessarily believing: http://answers.yahoo.com/question/index?qi...12095325AA45gGp