Currently Being ModeratedJul 14, 2012 9:11 PM (in response to brianwah)
Check the startup disk in case it needs repairing...
Launch Disk Utility located in HD > Applications > Utilities
Select the startup disk on the left then select the First Aid tab.
Click Verify Disk. If necessary, click Repair Disk.
If the disk is ok, try Starting up in Safe Mode. A Safe Mode boot takes longer then a normal boot so be patient. Booting in Safe Mode deletes system caches that may help.
Once you see the Desktop, click the Apple menu icon top left corner of the screen. From the drop down menu click Restart
If that didn't help, try Resetting your Mac's PRAM and NVRAM