First let‘s check some things:Please go to the Apple logo on the upper left of the screen, go to About This Mac, and tell me the System Version, the Processor and the Memory.Then go to Macintosh HD, then go to Applications folder inside that is another folder called Utilities inside that is an application called Disk Utility. Double click on that and when it opens you will see your hard drive on the left. Highlight your hard drive and click on Verify Disk on the right. If that is OK click on Repair Permissions. If Verify Disk is not OK let me know.