Weeellll...got a new psu (tested it, works fine) installed it, the lights come on on the computer, the CPU fan comes on for about a second then turns off, and the system fan runs at full speed. Holding down the power button refuses to turn the pc off. SO, I decided that I was going to unhook everything from the motherboard, even the ram, and test each thing out one at a time to see if it was any hardware, turns out that even with nothing hooked up to the motherboard but the psu, graphic, and the power button it still acts the same...which is why i'm thinking a short in the motherboard. Which would be weird considering there would be no reason for it and it's worked flawlessly for 2 years. Might I add that not even the bios comes up, the monitors are saying there is no connection detected.
You could try plugging in your old PSU without actually installing it in the case - just to confirm the PC is working fine. It sounds like a cabling issue with the new PSU. Is the main mobo PSU connector on both PSUs 24 pin or a 20 + 4 pin? If the system works with the old PSU then I'd carefully search for a cabling issue.
The first PSU would shut off unexpectedly, it was dying out. So I replaced it with a Rosewill Stallion Series RD400-2-SB 400W ATX V2.2 Power Supply. Half of the time the old psu would be dead and half of the time it would work fine...but when it was working fine the same problem would happen...cpu fan wouldn't work right, etc.
I just tested the old psu and it makes a whining noise when turned on and paperclip-tested.
So...we've gotten out of the way that it could have been a cabling issue since it's happening with both of the PSUs, the video card doesn't need an extra cable, all of the connections that need to be connected are connected. I checked the pins to see if some of them were bent and whatnot, none were.
CPU fan spins for a second, turns off. Monitor is displaying 'no connection', sys fan is running at full speed, holding down the power button won't turn the pc off.
(I checked to see if maybe it was the cpu fan by plugging it in to the sys fan slot, cpu fan works fine, it's the cpu fan slot)