Well you can try some basics such as restarting in Safe Mode per the directions in https://support.apple.com/en-us/HT201262. If the problem persists, you have have other issues. I'd start by restarting the computer in the Recovery Partition (Hold doewn Command + R on startup) and then install Mac OS on the drive it's currently installed on. It is possible your install was corrupt, this type of install will fill in an damaged or missing pieces of Mac OS. If you take this step, please ensure your back up is up-to-date and working as a safety precaution.
If the problem persists after all of this, please post back for further instruction.