Unable to boot into Mavericks OSX

[BruteForce]

My Macbook Pro Late 2011 was running fine after updating to Mavericks OSX, however after i do a restart on the mac, it is unable to boot properly. It is stuck at the apple logo with the mouse cursor. I have hard shut down the pc several times however issue still persists.
Anyone have any idea how what is wrong?

 

[havetobuy]

i think yr hardwares got problemo..
if u hav a mac osx thumbdrive..
used that bootup
goto DISK utility and doa REPAIR Disk
if still persist
reformat yr maverick OS

 

[B772ER]

Mac OS X: Gray screen appears during startup

follow the instructions in this article..