I have a 3 year old Macbook Pro (2.2Ghz Santa Rose, 4GB RAM) that use to be a great machine but it seems to have become slower over the years. I reinstalled Snow Leopard about a year ago but it's still pretty slow. Anyways, the problem I'm having is it will randomly freeze up for a 10-20 seconds (and I can hear the hard drive working), followed by booting me back to the login screen. When I log back in, everything is closed and it's like I restarted the computer. 99% of the time it happens I'm either clicking a link in Safari or trying to open a new page. I have tried multiple browsers, thinking it was an issue with the browser but it happens in all of them. Another time it occurs a lot is when I'm playing a video, especially in full screen. Any ideas what might be causing this? It's getting pretty annoying since it will happen at the worst times.