Step 1. Reboot your computer holding down the command-s keys. You should be dumped into a text mode. Wait until you get a command prompt (ie, text isn't scrolling, and you can type). Step 2. At the prompt, type fsck -yf. Step 3. Wait while the computer checks your drive. If it says your disk appears to be OK, type reboot. If it says "FILE SYSTEM WAS MODIFIED", run fsck -yf again. Repeat until it says your disk appears to be OK. Then type reboot. If problems were found and repaired, chances are OS X will run better now. Remember, fsck only detects and repairs minor disc problems. I'd highly recommend purchasing a professional disc repair programme, and I'd highly recommend not purchasing Norton Utilities, as it's notorious for destroying data, which is exactly what you don't want in a disk repair utility. My personal favourite is Alsoft's DiskWarrior.