Not know exactly what the user has attempted >.
Here goes anyways
Suggest the User start with Points 1 to 4 and then Test
Still having issues, move onto Steps 5 and 6 and Test Again
Still no resolve - move onto Step 7 and follow instructions therein
1 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.
1B - If using a Bluetooth Keyboard with Rechargeable Battery - Cable the Keyboard to computer for this unique purpose.
2 - Safe Mode will also eliminate Third Party Software, extensions and drivers from loading. It will only load the Minimum amount of Core Apple Processes to allow the the computer to function at a reduced Level of Performance
3 - Does the issue present in this mode ?
4 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.
5 - If not - there could be something in the main User Account playing up. To further isolate this - Set up users, guests, and groups on Mac. Then log out of the Main User account and log into the dummy account and test again if the issue persists.
6 - If the issue is present in the dummy account - then, this appears to be a System Wide issue on the computer.
Should None of the above work out for this computer >>
A - Have the computer evaluated by the Professionals who have the Special Hardware Software and Expertise to diagnose the issue and offer possible solutions
B - Make an Appointment at the Apple Genius Bar and have them evaluate the computer