Try Safe Boot:
- Shut down your Mac
- Wait until your computer turns off and after that press the Power button
- Right after you hear the startup tone, press and hold the Shift key
- Release the Shift key when you see a grey Apple sign and the progress bar below this sign
- After your Mac boots up, restart it as you usually do.
If this doesn't help, follow the instructions below:
- Shut down your Mac
- Wait until your computer turns off and after that press the Power button
- Right after you hear the startup tone, press and hold the Shift key
- Release the Shift key when you see a grey Apple sign and the progress bar below this sign
- Once you see Desktop, start a Disk Utility scan to detect and repair file system errors (don't forget to choose your main hard drive)
- Click on Verify Disk and then, if asked to fix problems, on Repair Disk
- After this, click on Verify Disk Permissions and then on Repair Disk Permissions
- After the process is finished, shut down your Mac and turn it back on after about 30 seconds
Apart from that, take a look at this Apple article and follow the instructions on Resetting NVRAM shown there: How to Reset NVRAM on your Mac - Apple Support
If these steps don't help, reinstall OS X. Make sure you are connected to the Internet. After that, follow these steps:
- Restart your Mac. Once it restarts and the grey screen appears, press and hold the Command and R keys.
- Select Disk Utility and click Continue.
- Select your startup disk on the left and click the Erase tab.
- Choose Mac OS Extended (Journaled) from the Format menu, enter a name, and then click Erase.
- Select Reinstall OS X, click Continue, and then follow the instructions on your screen.
If these steps don't work, contact Apple Support:
https://www.apple.com/support/macbookpro/contact/
