Computer won't boot

I went to turn on my computer after quite a while and it goes to the grey screen with the apple. The fan progressively gets louder and then i get a black screen with the message: disk0s3: I/O error.

Dec 31....Launchd: can't exec /bin/sh for single user: Input/output error

I tried all the ways i know to open the dvd drive to put in the installation software but i can't seem to get it to open....HELP!!!!! Thanks in advance....