Boot into Recovery (Command R) and from the dropdown menu: Utilities> Disk Utility> run the First Aid on your Macintosh HD. If errors are found and repaired, run again until no errors reported.
Latest Mojave Recovery a bit different—
Recovery: https://support.apple.com/en-us/HT204904
To get a good look at your System config. for conflicts or issues, you can run this utility http://etrecheck.com
If you need help interpreting the report you can post it here in its entirety in the "Additional Text" box in the edit toolbar below.
To trouble shoot further you can:
Try a SafeBoot https://support.apple.com/en-us/HT201262
Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc.
This test will tell you if third party interference; extensions etc are not loaded in safe boot mode.
Test issue in another user (or guest user) account https://support.apple.com/en-us/HT204443
This will tell you if it a universal issue or isolated to your user/admin account.
