Slow to load splash screen, failing system?

Recently after rebooting my PC the info on the screen would load very slowly. It would take maybe 2 minutes to get past the splash screen and then the OS would load slowly as well.

This first happened after I had been OCing my graphics card a few days ago. I was using the Unigine Heaven benchmarking tool and the computer froze completely in the middle of a test. I restarted my PC and it appeared to be frozen on the flash screen like so

http://i.imgur.com/4puH451.jpg

I shut it down and the next time I powered on it booted without error. Fast forward a few days later and this lagging splashscreen is happening all the time and I'm sure it's indicative of some other problem. I tried updating the BIOS and returning my OCed graphics card and cpu to their default settings.

Could my power supply be failing? my motherboard? Im running my OS on an OCZ Agility 4 which I purchased less than 3 months ago so I don't think it could be my ssd.

Everything seems to work fine after windows has loaded.

My Specs:


Windows 7 64 bit

Intel i5 750 @ 2.67 Ghz

12 Gb DDR3 RAM

Nvidia Geforce GTX 670

Gigabyte P55-UD3R rev.1 MoBo

Corsair TX 850 W PSU

Creative X-Fi Fatal1ty Championship edition Sound Card

OS is installed on OCZ Agility 4 128Gb ssd

edit: after some more troubleshooting the OS would fail to load completely. I thought that maybe my ssd had failed so I plugged in an old hdd (after messing about with the cables so I could plug it in) and was preparing to load Windows 7 onto it. I told the computer to boot from CD first but then didn't press a key when asked to boot from disk so it tried booting from my ssd... and it booted just fine without lag! now when when I reboot it's stuttering at the splash screen again but windows is loading fine

*bangs head against desk*

I've got no idea what's wrong. any help would be greatly appreciated