Hello. My name is***** to JustAnswer. I'm reviewing your question now, and will post back with your reply momentarily.
Try to start your mac in safe mode.
Start the mac and hold the left shift key.
Are you able to log in this way? If not,
shut down mac, start computer and hold command + R, select recovery drive, select reinstall osx.
Then follow on screen prompts for reinstall. it will not remove anything.
Let me know the results and we will go from there.
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