My 27 inch Intel I7 iMac has been running slow with spinning beach balls, loss of connection to keyboard and mouse and other problems. I installed a new version of OS and ran disc utility and diagnostics. None reported problems or resolved the issue.

Run EtreCheck and post the report here so we can check whether anything stands out in the report. This report will show us what software is automatically starting when you boot your Mac as well as summaries of system logs and performance metrics which may provide us with some clues to the problem.

Also, run DriveDx and post the complete DriveDx text report for each internal drive in your iMac so we can check the health of those internal drives. Within the DriveDx app, click on each internal physical drive listed and click the "Save Report" button at the upper right corner of the app window (this button only appears when the correct item is selected on the left pane of the app).

FYI, Most performance issues are either due to some third party software or a failing drive.

You should just be able to open the DriveDx report file in a text editor (default TextEdit), Select All & Copy to the clipboard, then Paste it from the clipboard into the bottom field of the "Additional Text" window making sure to fill in the first Title field before clicking the Save button. You won't be able to access the information in the forum editing window until. Click "Post" and you should be able to view the "Additional Text" item you attached. The "Additional Text" is available on the editing toolbar of the forum edit box and is the third icon from the right (fourth if you include the circle with question mark. The icon looks like a piece of paper and will show "Additional Text" when you hover the pointer over it.

I've never encountered any issues performing this action, although sometimes instead of the "Additional Text" attachment appearing as a drop down list box, it may just be a titled link which may or may not open in a browser (this is the only Apple forum related issue I've ever encountered with the "Additional Text" attachments).

Otherwise I don't know what is happening since I cannot see what you are doing nor the error you are receiving.

Edit: Most likely the SSD is Ok. The failing hard drive is more than enough to cause problems.

Also, here is how to use the "Additional Text" feature to add a copy of the EtreCheck report. Adding the DriveDx report is similar except you must actually highlight the text within the DriveDx text file report and select "Copy" as opposed to the "Sharing" option available within the EtreCheck app. Pasting the report from the Clipboard into the "Additional Text" field is the same for both.

You can use the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar.