Gateway Computer wont turn on?

I have a gateway desktop computer we lost power the other night and whn it came on I heard a pop noise. Then the computer wont turn on I have a single Green LED light on the Mother board but the computer wont turn on or do anything. I umed it was a Power supply so I replaced it, still getting the same results. I used a screw driver to byp the on / off switch hoping it was the problem but still nothing. What should I do next???