Type in services.msc in the Search bar from the Start Menu or a Run Dialogue, go to Themes, Right Click - Properties. Disable it and select OK. Then Stop the Service. Now set it back to Automatic and Start it.
Then try changing it to Windows Classic and setting it back.
Then try going to Control Panel - System - Advanced system settings - Settings (Performance) - Adjust for best performance, OK. Hit Settings (Performance) again and select Adjust for best appearance.
If the above doesn't help try an SFC Scan
You could also try restarting explorer.exe and dwm.exe.