YouTube

Try setting up another admin user account to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account 

Safe Mode - About

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply        Pastebin

Etrecheck – System Information

If AdBlock extension is installed, uninstall it.

https://help.getadblock.com/support/solutions/articles/6000055763-how-do-i-install-adblock-how-do-i-uninstall-adblock-

Apple Support article: If Safari is slow, stops responding, quits unexpectedly, or has other issues

You might want to consider starting a new discussion. Since this one is marked solved, less people are likely to look at it. A new post would be much more visible. You can link to this one.

It may not help, but try running/posting the Etrecheck report. The program was created by Etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply        Pastebin

Etrecheck – System Information

If I have no Safari extenions installed & I've tried reinstalling flash, cleared caches, restarted in safe mode and I'm still unable to play youtube videos in safari or chrome on my iMac, any suggestions what else i can try?

Thanks in advance.

You are welcome.