I suggest you boot a "Live CD" to get a running host.
Then find your data. If you find it, copy it to an external disk or another host. Finally do a complete fresh install, and set up a backup solution.
If you can't find your data, (and presuming you don't have a backup) make a decision now about how important it was and whether its worth trying to recover it. Undelete may be possible as long as you don't keep writing to the disk. Something like
ddrescue might find some more data too. Or if it is business critical then you might have to pay for professional data recovery.
The other option is to pull the old disk and do a fresh OS install onto a different disk. Put the old one aside for data recovery purposes later, and work on getting a live system up.
Then set up your backups so that in the future you have better options, should something like this happen again.
Good luck !