Last year I did a clean install of Snow Leopard (wiped the hard drive, and started with a new OS) I am finding that from time to time the system runs incredibly slowly for simple tasks (like selecting a different window). I have checked that I still have enough room on the hard drive (100 GB free space on a 250 GB drive). There is 4 MB RAM (no room for more). The processor is Intel Core 2 Duo 2.16 GHz. Just lately, the system has frozen a few times, forcing me to simply turn it off and reboot. It has also been reluctant to let me log in again - I get the initial screen that lists the users, and when I click on my username, the box to allow entry of a password never appears - all the options to sleep/restart/shut down are greyed out, and it just sits there. Eventually I do get in, but I am concerned that the day is coming when I can't get in at all. What diagnostics or repairs can I run? Are there any repairs I should be doing on a regular basis anyway?