You can try uninstalling Support Assist and then reinstall it to fix the “SupportAssist not working” issue. To do this, follow the steps below: Step 1: Open the Settings application and open the Apps part. Step 2: Now, find Dell SupportAssist and uninstall it. Step 3: Once the uninstall is completed, restart the system and then reinstall the latest version of Dell SupportAssist from the Internet. Then, check to see if the “Dell SupportAssist not working” error has been fixed.
[IMAGE]   EVERY time i try to complete diagnostics, quick test or full test, it fails.  see pic desktop, win 10, inspiron 3880 contrary to msg, there are no other tests running; started test after reboot.    
diagnostic online tests fail every time