We need to know what version of OS X you are running.
You may want to run these "standard" fixes if the problem persists.
1) Check the amount of free space on your harddrive. You should have a several gigs free.
2) You should run disk utility
a) verify the disk
b) update your permissions.
3) Try a safe boot.
Shutdown your machine. Hold down the shift key. Poweron. Wait awhile Wait awhile while you harddrive
is being checked.
Here is how to find out what version of Mac OS you are running:
Click on the blue apple in the upper left hand of the screen.
click on this icon
Click on the first line, "About This Mac"
Most of these are numbers & that's what we want.
What version & Processor do you have?