Computer won't turn on

I know that is a broad question but I'll specify a little bit.

I have a dell studio 540 s and it ran fine. One day it just didn't turn on.

So through my own efforts I have checked the power supply by plugging in a paper clip from the green to black wire on the big connector that comes out of the power supply box. The fan turned on so the power supply is good.

Next I though that the power button itself wasn't working so I removed the connector from the power button to the mother board and tried to manually touch the pins together to try to turn it on ( I used a metal screw driver with a plastic handle to touch two pins together but nothing happened)

Next I reset the Bios password by changing what 2 out of the 3 pins were connected where it said "CMOS + PW"

But nothing has worked so far if you have any ideas please let me know.