I have an iMac that I bought new in 2010. It's build date is mid-summer 2010. It's the basic model I3, 4Mb RAM, 500Gb HD. I'll write what has happened in bullet form, that might be easier to read. What I am wanting to know or confirm in my own mind is that my hard drive is on it's last legs, stumbling to the end. Zero problems from the time I bought it, October 2010. On the computer many hours per day, 7 days per week. Crashed and would not reboot Thursday, May 4th Tried all the suggestions to free up hard drive space, re-installed macOS Sierra Friday night and Saturday everything was slow, from typing words, opening programs, with a lot of hangups. Sunday morning May 5, I erased the hard drive, reinstalled macOS Sierra, restored my files from my Time Machine backup Moved Photo Library to external drive, deleted that library on the internal drive to free up max space I currently have 60Gb total on a 500Gb hard drive. This morning it went from working well to very slow, freezing, but not turning itself off. About the time I think it's time to go buy a replacement, it starts working perfectly with no issues. I ran Disk Utility Repair tonight ... no problems with hard drive. Right now as I type this, it is fast with iTuns playing music, a couple of Excel sheets open, Apple Mail is open and the Time Machine is backing up without problems. I did unplug all external drives and turned off Time Machine to see if that had any affect ... it did not make a difference. I have tried Safari, Chrome, Firefox, Opera and all of them at times will hang. My MacBook Air wifi off the same network is extremely fast with zero problems. Saturday as a test I turned off my internet router ... went straight Word and Excel, and it was so slow that words or numbers were not showing up as typed and then would appear slowly, one digit or letter at a time. I forgot to list what is did/does when it's not running perfect. Any program that is opened will "not responding" Open Finder .. "not responding" As I type this ... it is back to being bad ... type and no words show up, then after a minute or two words will show up very slowly one letter at a time. I tried to backspace for a correction, it hung up. Internet pages will not load, curser moves between two monitors but everything is frozen so it will not accept the clicks of the mouse. Hung up at 3/4 progress bar on start up. Once on Saturday and again today, after it booted up both screens went black with a moving cursor in upper left corner ... I let it set that was for as long as it wanted ... once I had to power it down, another time it eventually went from the black screens after 10 minutes and finished the start up ... ran normal after that. I cannot think of anything else I can try. I was sure reformatting the HD would take care of any hidden issues. Any help, suggestions are appreciated.