We can try some basic troubleshooting steps and see if that works or not.

Reset PRAM and NVRAM (Solution 1)

1. Shut down your Mac
2. Locate the following keys on the keyboard: Command, Option, P, and R.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears and before the chime sound.
5. Hold the keys down until the computer restarts and you hear the startup sound for three times.
6. Release the keys.

Restart in Safe mode (Solution 2)
Make sure that the computer is shut down. Press the power button. Immediately after you hear the startup tone, press and hold the Shift key. Release the Shift key when you see the gray Apple and progress indicator. Let the Mac boot up...


Run Disk Utility in Single User Mode(Solution 3)
Turn your Mac off. Turn it back on and this time hold down the Command (Apple) key and the S keys at the same time. Then type the following command...

/sbin/fsck -fy (note the space between fsck and -fy)

If you can't run /sbin/fsck - fy then type only fsk - fy

Hit return and the disk utility should run and let it finish. When it finishes and there is no error, then type reboot and hit return. Let the Mac boot up. (Disk Utility will fix all system errors, bad preferences files etc)

Let me know if that didn't worked. Only click Accept after we solved the problem