Did you reciently load on a new piece of software? plug in a new camera or something of the sort? I did this on my desktop once, and it messed with one of my hard drives so that it didn't show up. I had to reinstall the motherboard and drivers for that and that fixed it.
Other things you can try are the following:
1. Back up all the files on your computer at the moment
2. Do a system revert via the help section. If this doesnt work, revert it back to the current position
3. Try using data retrieval software, you can find some free on
www.download.com4. If none of these works, and no one else has any ideas, you can find a computer shop and they should be able to retrieve the data for you.. for a price.