Start with this if IntelMac...
Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes or more.
Delete this file...
/Users/YourUserName/Library/Preferences/com.apple.dock.plist
Apple hid the Users' Library folders...
Method 1:
- From the Finder, select the Go menu at top of the screen, and choose Go to Folder.
- In the window that opens, enter ~/Library, and click Go.
Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.