If you remember when the issue started you can use a system restore point dated before the trouble.

Therein is the problem, it's been a while now an I'm only just looking in to it now I have some time off from work. I've updated the first post a little.

I'll keep at it. It just seems like something is causing my system to hang, with this much power that shouldn't be the case.

With those symptoms there is no quick way to identify the culprit. Try disabling sli and physically removing one gpu. And try removing some ram sticks as well.

Could also be adware / virus that your antivirus isn't picking up.

You could try loading up a live distribution of Linux and seeing if you experience similar issues. If you do, you know it's a hardware issue. Given a similar situation, I'd be tempted to back up the important stuff, wipe the box and just go back to a clean install of Windows.

If that's not an option, you can go through and just remove all the applications from add/remove programs that you don't really need, defrag your non-SSD drive, run CCleaner to try to clean up some of the cruft. Though you've already run CCleaner, so I dunno how that'll work. Pretty bizarre issues considering how ridiculously specced your box is.

Does the windows 8 disc have repair option?

http://www.bleepingcomputer.com/tutoria ... c-repair-/

Well, (sorry for the slow reply) this issue doesn't really happen any more - so I think it's possibility just a compatibility issue with an update that has since been fixed - however, I'll keep an eye on it and see if it resurfaces, especially after the next wave of updates, or updating to windows 10.