Something Wrong with PCI slot.

Hello,
I have been facing a video card or display problem with my computer. So, I decided to change settings from BIOS therefore I changed my display to read PCI . Because, I had only modem in PCI slot. But it was AGP. Than, I over clocked my computer in BIOS. The afterward changes really messed up my computer. Now the computer does not turn on at all. But fan and the heat processor are still running. Looking for solution.
Thank you.
