Why does my mac stop downloading files, copying to clipboard, saving files to desktop, etc? iMac g5 1.9 ghz 17" running 10.5.8. Had a hard drive crash and bought a new one. Loaded new OS leapord. Everything works fine at first, but after the computer has been on for a while, it will stop downlading files, disk verify doesn't work. I can't copy and paste stuff. It seems as if the hard drive is full, but I have only used 32GB of 300GB. When I restart, it works again, then slowly not. Is it an overheating issue? How do I know if my fan is running? Is it a bad hard drive I put in it? Bought it new with three year waranty. What's wrong? Please help.