A month ago, my iMac woke up and was really slow to open some websites. I thought it was because the cache was full because I had been running 12+ tabs the night before, so I decided to restart the machine. I could never get past the grey startup screen after that. Took it to the Appple store and they wouldn't work on it because it was "obsolete". They ran the the short version of the hardware test and said something was wrong with the RAM. I replaced the RAM with RAM I knew was good and nothing happened, still couldn't get past the gray screen. Took it to a local shop who would work on a machine this old. They determined that the hard drive had gotten corrupted. They wiped the drive, reinstalled from the backup and everything was back up and running. Worked great for about a week, then I started getting the spinning wheel of doom on a random basis. Sometimes, like now, I'm getting the wheel every 5 seconds for absolutely everything I do. Sometimes I go for days at a time and get none. I have run the Apple Hardware Test and it finds nothing. I've verified the disk, I've verified and repaired permissions and SMART status says Verified. If it's a failing hard drive, I have no problem replacing it. If it's a logic board, I'm getting a new iMac. This machine ran flawlessly until a month ago and I'm at a loss on what to do or what to check. Anybody have a clue what might be wrong or is there anything else I can check myself? I know just enough to be dangerous and don't know enough to actually troubleshoot it myself.