iMac freezing
Hi, I have a 21.5" mid 2010 iMac with High Sierra 10.13.6. The computer keeps freezing and showing the colored pinwheel. It occasionally works fine. Works fine in safe mode. If I unplug awhile, then it works fine also. But ultimately regresses. I've redownloaded OS and then it worked fine for awhile, but then regresses. Any one have an idea how to fix it? I would prefer not to have to buy a new one, but I recognize that this one is getting long in the teeth. Thanks,
iMac 21.5″, macOS 10.13