Mid-2011 21" iMac running OSX 10.8.5. 1TB HD, using 160GB. 16GB memory. Intel i5 2.5 GHz CPU. I have read the stickies and followed their advice. Searched and found some past relevant threads and followed their advice (although without a solution). Hopefully I've followed due process. Beachballs constantly, usually only minutes after restart/reboot. Just before the beachball appears, the mouse pointer can still be moved and the clock in the menubar will still tick but I click on apps in the Dock and they do not open and click on open apps but cannot switch windows to them. Incipit beachball. Observations I have made: I have tried to watch the Activity Monitor closely. It sometimes shows that when opening an app or a new tab in Firefox or Chrome, CPU use sometimes exceeds 100%. These instances -- at least the ones I have observed -- do not precede crashes. I cannot detect any pattern indicating that any particular app opening/usage has an effect on crashing. In fact, if I simply log on and open nothing (including with no login items loaded) the beachball will inevitably appear. I have watched the Activity Monitor's memory usage and page ins/outs right up until crash time and nothing seems to hog memory or generate many ins/outs. (Oddly, "VM Size" generally bounces between 250-300GB -- how could I have that much virtual memory?) No new apps installed in the last several weeks. Troubleshooting steps I have pursued: I have updated OSX and every app downloaded through the App Store. I have also updated every other app I can find an update for. I have reset the PRAM and VRAM and SMC. I have run the AHT full/extended test without errors. This would suggest that the issue is not hardware. Full boot without peripherals connected still crashes. This would suggest that the issue is not peripherals. Safe boot avoids crashes if it is a full safe boot, but if I safe boot only to exclude login items it still crashes. This would suggest a kernel extension or font issue. I have therefore run the font book check for errors utility, but without any error result. (Interestingly, safe boot at startup wires 14GB of memory in Activity Monitor. System acts sluggish. Is that how it's supposed to work?) Logging on as a Guest User or with a dummy account still results in a crash. This suggests that the issue is not a login item or a non-Apple app or a corrupt preference pane. I have used Console to try to identify any consistent, particular use/access/error message/activity around crash times and cannot detect any particular pattern that precedes the beachball. I'm not an expert at interpreting the logs/reports but there doesn't seem to be any pattern/correlation to any particular app or system action or anything. I have verified the HD using Disk Utility (in Safe Mode) several times. I have also cmd-S booted the HD and run fsck -y tests of the HD that have not revealed errors. I also rebooted with cmd-R to run Disk Utility and it repeatedly finds no errors on the HD. I have verified and repaired permissions several times. There are 21 permissions which will not repair (i.e., show up as errors when verifying even after having attempted to repair them). Most are iTunes issues, 6 are Safari (which I never use), one is a JAVA issue (which is disabled), and one is a ARDAgent reference (I don't know what this is). Perhaps important information: I did have the HD replaced about a month ago with no issues up to this point. I also have had weird, very brief screen white flashes in the evenings for months. I had the repair techs run a test on the video card and display when the HD was replaced and that returned no error message. But the "flashes" continued. They do not correlate in any detectable way with the beachball. The Bootcamp partition of the HD functions flawlessly (including no screen flashes), suggesting that the issue is OS X based rather than hardware. Strangely, the beachball seemed originally to prefer to appear later in the day. I could often work until late morning or early afternoon without issues. Late at night, the beachball appears within 5 minutes of reboot. I have disabled the functions and apps that specifically come into play later in the day (f.lux and OSX's native adjust brightness option) to no effect. Still beachballs, and the time of day is increasingly irrelevant. Any next steps? I have full backups in the cloud (Crashplan) and on my external HD (Time Machine). I am concerned that restoring from Time Machine or Crashplan will restore a system corrupted by whatever has my current system bogged down and on its way to the same issues. Thanks a bunch for any help/suggestions.