black screen at startup

When I try to turn on my macbook, it eventually goes to a black screen with "disk0s2: 0xe0030005 (UNDEFINED).
localhost:/ root#"

Any idea how to get it to start from here? I've tried holding shift during startup and i've tried command option pr, that all still brings me to this screen

Tray booting up from your install disk (press C)

When the restore, install comes up select Disk utility from the top menu and try repairing the disk first

if you can manage to back-up your files to an external - do so

Is it still under warranty - might be the hard disk is failing

of course, i can't find my disk anywhere. Any other suggestions?