I own a iMac Mid 2007 (2.4Ghz, 320GB, 2GB) and in the last few weeks it has been running very slowly. It takes about 3 to 4 mins to boot and only lasts about an 1 hour before Finder freezes and requires a reboot. When I try and reboot it gets stuck on the grey apple screen and never loads. But when I try about an hour later it boots up in 3 to 4 mins. I have Repaired the Hard Drive and Permissions but this does nothing. I have only used about 45% of the Hard Drive. Is there anything I can do to get it back as a normal working Desktop Mac?