I was playing my game and all of a sudden everything, including the SOUND, starts skipping. Everything is fine if im not loading something or moving it seems but if I am, it begins to run SLOW until I stop. I dont understand how this happened because I've been playing this game for 6 months and all of a sudden for no reason, everything is running slow.   So I exit my game and restart the COMPUTER but during start up I see this message in DOS. "Warning CPU has been changed please re-enter cpu setting in cmos setup and remember to save before quit!"
    I skip the setup and go to WINDOWS and everything is still running slow, this appears to only happen when I open a program or a folder. My mouse begins to skip ACROSS the screen for a couple of seconds and then my computer returns to normal speed until I open a program or something. I ran some of my virus scan but nothing showed up. I really have no idea what is going on.  
    So I restart my computer again but this time nothing shows up on my screen. The computer is running but my screen is black. After another couple restarts, I can finally see the screen and everything appears to be running smoothly in windows now. I really have no idea what is going on.  
     If someone has any idea as to what is happening, please help.  Are you overclocking your system?

You may need to remove excessive dust from your heatsinks and fans.