"I have an Intel 24" Imac (late 2008) that was giving me lots of problems although it worked fine if I used a second external monitor. "

But at that point you didn't reveal if you had that issue fixed. I'm guessing you did not and now want to start a career in PC repair. Since the power support can be swapped out and may be the cheap part you are following some one's sage advice. Try the cheap parts first.
Bob