My computor works for a while and then stops responding

Hi, I have been having trouble with my computer lately with blue screens, high disc usage, slowness and freezes. It turned out that I had a lot of programs running when I would start up and I have stopped most of them. I am no longer getting the blue screens and the high disc usage alerts, and the computer is much faster. However... every once in a while (maybe every hour or so) it still freezes up for about a minute, then starts responding again.

I have a Windows 7 Home Premium eMachine.

Can anyone help me?