4 pin cpu power socket causes pc to not boot

Hey guys. My pc had shut down a few days ago and I narrowed down the problem today. Everytime I plug in the 4-pin power socket on the motherboard for the cpu, the pc does not boot at all (no fans running etc). When I unplug the cpu 4-pin on the motherboard, everything is fine. The fans run at their at their normal speed (led and gpu). Obviously, there is no post since the cpu is unplugged. Did my cpu 4-pin power socket short circuit? I tried putting an old cpu in (athlon 3000+) but the same problem occurs. Thanks for any help!

My specs are :
Amd Opteron 180
MSI K8N Neo4 platinum motherboard
2gb gskill ddr-400
ati 3870

Just want to throw this out there since no one else mentioned it, I ended up fixing my infinite boot cycle by using the "jumper" pins for the CMOS to reset it. I didn't know of this until some more research after the post above. Somewhere on your board should be a couple pins labeled something to do with "CMOS". Grab a screwdriver (flathead worked nicely for me) and touch the two pins at the same time, effectively shorting out the CMOS and forcing the BIOS to do a reset, it seemed anyway. Afterwards I booted and was given a screen of choices, I went with last known working, and up came BIOS.