Computer runs fine for 2 days then suddenly freezes?

So iv had a home built computer for little over a year now and I am having a small problem where now all the sudden it freezes? I have a i5 2500k that use to be running at 4.4 but i clocked it down to 4.2 since the random freeze, 24 Gigs of Ram running at 1600, and a GTX 550 Ti GPU, im not sure what would be causing this. I havent had this problem b4, only thing i have done recently is Overclock my gfx card a little but everything worked fine when i played BF3 for 2 hours and suddenly when im looking at imgur and talking to a friend on Skype my whole computer freezes. (I ruled out that it wasn't my keyboard or mouse after I realized i had been talking to myself for 5 minuets raging that my mouse and keyboard stopped working....) LOL jk... anyway

Anyone have an idea?

O! i also am using the beta nVidia driver!