Mac book air disk error

Ive got a MacBook air and when I came to turn it on today an error
appeared saying disk error press any key to restart. I've tried restarting while holding the option key and the only difference before the error appears is it takes a second longer to appear. No help screen appears I've also tried to load my mac osx disk with a USB cd drive but that refuses to load. Really need this sorted any ideas?? As I've searched the forum and can't find any that I haven't tried at the moment. Many Thanks in advance