You may try to restart your computer in Safe mode by taking these steps:
- Click on the Apple sign() at the upper left corner of the Desktop, select 'Shut down' from a drop-down menu;
- Wait until your computer turns off, then press the Power button(⌽);
- Immediately after you hear the startup tone, press and hold the Shift(⇧) key. It should be held as soon as possible after the startup tone, but not before the tone;
- Release the Shift(⇧) key when you see a grey Apple sign() and the progress bar below;
This will force the system to perform several maintenance routines and load essential system software.
Once you've seen the Desktop, start a Disk Utility scan to detect and repair file system errors:
- Open Disk Utility application:
1. Click on Finder at the bottom of your Desktop;
2. Select Applications folder from Finder's left sidebar and then open Utilities folder (or press Command(⌘)-Shift(⇧)-U), double-click on Disk Utility icon;
- Choose your main hard drive from the left sidebar ('Macintosh HD', usually);
- Click on 'Verify Disc' at the bottom right corner, your Mac will perform a diagnostic test. Click on 'Repair Disk' if prompted to fix problems, or follow instructions given on the Disk Utility window;
- Once the routine finished, click on ""Verify Disc Permissions"", after it's done, click on 'Repair Disc Permissions';
- Wait until the process's finished and shut down your Mac, turn it back on in 30 seconds;
If this will not help try to
Reset SMC.
http://support.apple.com/kb/HT3964
Hope this will help