Check you hard drive: Reboot into the Recovery HD by choosing the ‘Apple‘ menu > Restart, hold down the ‘Command’ + R’ keys on the keyboard during the start up process when you see the Apple Logo you can let go. When the machine boots eventually you will see the OS X Utilities screen., select the Disk Utility and then select Continue. Then in Disk Utility select Macintosh HD in the left column, if there are two or it is named something else choose the first indented item, and then select Verify Disk on the right. If that is OK in green type then select Repair Permissions. If it is not ok let me know.
If all is ok use this software to clear your Preferences: