wont start- 'disk not recognized'?

[madeleine]

I own a Macbook, OSx, just bought six months ago.

It was acting slow so I restarted, and now there is a black screen that reads:

diskOs2 0xe0030005 (undefined)
Jan 30 10:07:22 launchd: can't exec /bin/sh input/output error
disk not recognized

what do i do??

thanks,
madeleine