SIDEBAR ICON NOT WORKING

So when you click on the Sidebar icon there's nothing showing in the sidebar, right?

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Please read the following user tip and restate your question/problem in detail: 

     Writing an Effective Apple Support Communities Question - Apple Community

What sidebar icon? Generally if it's not working drag it out of the Finder's sidebar, find the item it represents and drag it back into the sidebar.

If this is not what you're referring to more info would be helpful.