Computer Freezes in Team Fortress 2?

Whenever i try to play Team fortress 2 or Fable 3 my computer randomly freezes in the middle of the game. i have to alt tab back to desktop and click the game icon again to get it working. even after that it still continues to do that. Sometimes it will wait awhile before it freezes and sometimes it will freeze instantly right when i get back from having it freeze. It continues to do this throughout the entire game. I have a dual core processor and windows 7 32 bit. my graphics card is a Geforce GTS 450. I recently just had a 1 tb hardrive put in and also 6 gigs of ram. I also noticed that whenever i bring up something like a game or sometimes even internet explorer that my new hard drive makes a weird noise. Please help.