Just recently, I have been play Deus Ex: Human Revolution, DayZ, and Skyrim, and my system seems to pick up the habit of lagging. It has never done this, and I haven't done anything to it.
AMD FX-6100 Not OC'ed
8 Gb's RAM
LEPA 500W PSU
Seagate 500Gb HDD
And the GPU.
I have dual monitors, but I don't think it'll matter.
And, I know there will be people that will say "Oh, its your faildozer CPU. Throw it out and get an i5/i7. It has NEVER lagged before. Playing skyrim on Ultra with no fps drops or choppiness. "