Computer overheating?

I can typically turn this box on in the morning and use it for a couple of hours (usually playing games) and interesting things start happening.

Usually the first thing that the mouse cursor starts flickering, progressively increasing to the point where it flickers every 1/10 of a second.

If I keep using it my USB headset starts crackling and giving *very* bad quality sound (still works).

I find that if I reboot my PC it goes away, but will then come back within 1 hour (where the initial instance will take a 5 or 6 hours to manifest).

I recently purchased and installed a GTX 660, it appears to work perfectly, but on my old card (GTS 250) the mouse cursor problem did not occur.

One interesting thing to note is that the games I am playing should not stress this card - at all, primarily I play League of Legends and maybe a few more intensive games such as BF3.

Any suggestions or help would be appreciated.
Darkedge.

EDIT: I just noticed that logging out and back in will also correct this issue (discovered this through experimentation).
I've also managed to link the mouse blinking starting at a similar time to when I share my screen on Skype, but this does not stop when I stop sharing my screen.