I have iMac 20" (2007) model. I have come across 4 problems with this iMac now. 1. Random clicking sound, sounds like it's coming from the screen or something. Done a hard drive test using the Disk Utility. Says Verified for S.M.A.R.T. Done Verify and Repair and it states OK. 2. Sometimes randomly the whole system will freeze but the mouse will be moveable but nothing can not be clicked as it won't respond. So I have to power off holding the power button. 3. Opened Safari and all of a sudden screen went black. Pressed keyboard buttons, moved mouse nothing worked. Screen still black. 4. Once I turned the iMac on it made the chime sound in beginning but screen was black. Had to hold power button and turn it off and then powered it on and it started working like normally. I've done smc and pram reset. I am guessing it's the hard drive that's coming to it's last breath?