imac freezes every few minutes

[itbek]

Hi, I have an imac I purchased two years ago. Recently it started getting pretty slow and sometimes frezzes for a few seconds. Then I tried to update to High Sierra but the update got stuck, and when I tried to reboot the mac' it wouldn't start. I had to erase the whole computer and install a fresh os. Idid it and the mac worked fine for a few weeks. But two days ago its started freezing over for a few seconds every 10 or so minutes. Everything becomes unresponsive except for the mouse and audio. So if I'm watching a video the image freezes but the audio goes on. It's super annoying!
I tried closing every app except one so there won't be anything running in the background taking up CPU, but it didn't help. So I don't think it's a RAM issue but I'm not sure. And as I mentioned, I just reinstalled the OS. Any idea what could be the problem?? Maybe it's a software causing this? Or is something just wrong with the hardware?
Please Help?

 

[casperes1996]

Try and run Apple Hardware Test and see if it reports issues

 

[chscag]

Was the iMac you purchased new or used? You didn't tell us the year and model - which always helps when you post to a forum. It does sound like it may be that the hard drive is failing. Boot to Recovery (command plus r) select utilities, Disk Utility, and run First Aid on your Macintosh HD (bottom entry not the top) to see if any errors are reported.

 

[itbek]

Was the iMac you purchased new or used? You didn't tell us the year and model - which always helps when you post to a forum. It does sound like it may be that the hard drive is failing. Boot to Recovery (command plus r) select utilities, Disk Utility, and run First Aid on your Macintosh HD (bottom entry not the top) to see if any errors are reported.

Thanks for the tip,
The imac was purchased new. The year is 2015 and the model is: 21.5 inch, 1.6 ghz processor, memory is 8gb 1867 MHz DDR3. (I'm not sure if these are the relevant details)
I'll try doing as you suggested.