There's no disk in the drive tray, and the computer isn't shutting down randomly. I keep it clean outside but it could be dust because my desk is next to the firewood storage by the fireplace/woodstove.

With better light tomorrow I will open the cabinet to check it out, vacuum, and blow things off as I can.

Thanks everyone for the suggestions. I'll let you know what I find, maybe with pictures. I can buy another computer, may do that and keep this one for storage backup. We did a backup to a seagate external drive last week.