Until the last month or so, my computer has been freezing and just randomly the mouse and keyboard would not work, while the computer was still running. When I restarted the computer, the problem still persisted... I would leave it off and after a couple hours it would work.These problems only occured in games.
Though that stopped happening about a month ago, but now I have a ton of lag in all games. It isn't performing close to what it used to. I have run spyware and virus scans, and came up with nothing... Fans are all on...
Well, for starters, I would pull one of those sticks of RAM off the board. If the board runs dual channel and you've got three sticks, it more than likely will cause problems. Even if you have two sticks 1X1 and 1X512, remove one or the other and see how the machine operates.
What kind of PSU do you have and hold old is it? Maybe its decided to go bad. What kind of a board do you have and do you overclock? It sounds like something is going bad in the machine, something is not adjusted right in the BIOS settings or something is throttling your system due to heat. Try cleaning out the case thoroughly. Get rid of all dust and make sure all the fans are running.
Running 3 sticks of memory? Some boards won't work properly with 3. I'd pull one and run just 2 in dual channel mode. If that doesn't fix your freezes, try memtest, a free download to check for errors.