how to restart my scrolling imac.

When i start my imac the apple comes up and then screen icon just scrolls. any suggestions? I checked the OS X UTILITIES harddrive by restarting it with Command "R" and it said "the volume Macintosh HD appears to be ok. . i relaunched the OS Xsoftware, but when i restart the computer it doesnt the same thing all the time. can anyone help here?