i'm experiencing a very weird problem. my build is fairly new...i5 2500k, 8gb RAM, and this week i added a 7850 OC. i am running win 7 64-bit.
so here is the problem i've noticed in the last few days. i'll come home for lunch from work, turn on the PC (shut it down at night) and play BF3 or Dirt 3 and get an average of 60fps in BF3 and 65fps in Dirt 3. i use fraps to determine this info.
then i leave the computer on, go back to work for a few hours and come home and play again. this time i get 50fps in BF3 and 45fps in Dirt 3. i have even played the same map in both with the exact same timing on benchmarks and seen this difference. if i restart my computer, immediately my FPS increase to the normal rates in those games.
what's even weirder is that if i run 3dmark2011 either right when i start my PC or 5 hours later when i seem to have FPS problems in game, i still score the same at about 6,100. i cannot figure out what's going on at all. maybe it's a driver issue? i have the latest for the 7850, but i know that's a new card and maybe there are some bugs. it doesn't sound like a hardware problem though.
I can't be sure about what exactly it is but if you leave your computer on for long periods of time it does seem to become bogged down. I don't know why some people like to leave thier Pc on 24/7 , I don't believe it's good for it unless the computer is doing something.
Do you have a screen saver enabled on yout Pc?
Unless you have a slow loading computer and your pressed for time I would just shut it down when your done and start it up when you come home. It would be eqasy enough to turn it on when you walk through the door and then by the time your ready to play it's up and running.
As far aas it being a driver issue you can always roll back to the previous driver to see if that corrects the issue.
im going to preface with: i have no idea but am interested. im actually curious if i would see something similar if i bothered to look and just havent been as observant as you or had as much opportunity. i leave my computer running for weeks. my setup is very similar to yours.
i will however open the floor with my initial thoughts. what sort of software do you have running in the background. do you use an antivirus program of some sort?