Original post by: Vishal Chaudhary ,
did you messed up with the drive recent? the '?' symbol indicates that Mac is unable to locate system software to load the OS. Before your Mac froze up did you noticed any unusual drive behavior like some clicking sound?? Disk Warrior is a great tool but tool will not overcome any physical damage caused on the hard drive components. They can cure the logical ones. Would suggest you to try simple steps to cure th issue: http://support.apple.com/kb/TS1440?viewlocale=en_US Otherwise you might need a technical expertise.