Black Screen...

Hey all. I recently switched out my graphics card (I had a 7970 for a bit, but decided that really I should put the money towards other things) so I put my 460 GTX back in, but now I'm getting a black screen with a blinking cursor. my question is this: what are the possible causes? I can get to the BIOS, but nothing beyond that. From what i've gathered, my potentional causes are as follows...

1. bad RAM
2. Improperly seated GPU
3. Failing PSU
4. Failing HDD

I have a hard time believing that my PSU, RAM, or HDD failed when I switched out my GPU, but sadly i'm @ my parents for the weekend and am unable to play doctor with my computer. Just wanted to see whether or not I should stop by Fry's on the way home to pick anything up. I realize that I'm not providing a whole bunch of information, so I'll go ahead and put specs etc down below.

CPU: i5-2500k (OC'd to 4.3)
Mobo: Extreme 4 Gen 3 P67 Asrock Board (I updated the BIOS just in case)
RAM: I have no idea the brand, but it's 1333 DDR3 RAM (8 Gigs)
GPU: 460 GTX
PSU: Corsair 650
HDD: 7200RPM 320GB (main drive, with OS on it) 5400 3TB drive (video and music) 7200 500GB (Photo)



thanks in advance for any advice!