it might be a filesystem problem on your disk. You can try this to see if will fix the problem: boot your MacBook Pro into Recovery mode by holding down a Command key and the R key as it starts up. Once the Mac OS X Utilities menu appears, select Disk Utility. On the left-hand side of the Disk Utility window, select your internal disk’s boot partition (typically called “Macintosh HD”). On the right-hand side, press the Verify Disk button if it’s not greyed out; if it is greyed out, or if it reports that errors were found, press the Repair Disk button. Once the verification/repair is completed, exit Disk Utility and select Restart from the Apple menu to restart in normal mode. Log in as normal, and try selecting Restart… from the Apple menu; does the beach ball still perpetually spin?