Well, discovered that my weird PC problem is not, in fact, overclock related. To reiterate:
On cold boots, my PC often has to try twice to start. Right after I hit the start button, it will start up, shut down before the post screen appears, then start again successfully. Then, at Windows login (Windows 8 preview), none of my USB devices will work, and I'll have to hit restart once before I've got a working keyboard to log in with. Once I'm finally into Windows, everything runs great. I can run Prime95, StressCPU2, and any game for hours without a hitch, and I can run Folding@Home for days without any issues. This occurs on stock clocks and persisted after I reset my BIOS to undo any settings I've changed.
Here are my specs:
i3-530 w/ CM Hyper 212+ Cooler (no longer overclocked

)
ASRock H55DE3
Sapphire Radeon 6850 1GB
8GB Ripjaw X DDR3 1600
500GB WD Caviar Blue
Seasonic X750 PSU
CM Elite 430 Mid Tower
Going to test with my spare PSU tomorrow, and if the problem persists (I'd be rather upset if it was the PSU, considering I picked up this Seasonic a couple of weeks ago for the bump in wattage and quality over my CX430), then I'm assuming something is up with my motherboard or CPU. Of course I don't have spares to test with, so that's a bit of a dead end. Any suggestions? Honestly, might just throw care to the wind and pick up a 2500K and 1155 motherboard at that point.
Edit: CX430 didn't change anything, so it looks like it isn't my PSU.