My iMac G5 is starting to really act up on me. Among other sluggish symptoms, when I put the pointer at the edge of the Desktop for the Menu to "appear", the menu doesn't roll onto the screen like it's supposed to. The menu icons also don't zoom as I roll over them. It's been 3 years since I purchased the iMac and have never done maintenance or cleaning. How do you perform maintenance on the OS? Should I buy an external HD, backup everything, and totally reinstall the OS? Any help would be greatly appreciated.