Well, run chkdsk on your C drive and have it "scan for and attempt recovery of bad sectors", which is basically a surface scan. Just to be sure that part is safe.
Something may be corrupted. Or you may have a virus if you aren't running a virus scanner. You can do a free online scan at
www.antivirus.com. The drive may be failing. You may have encountered a "malicious" script on a webpage that managed to format the drive. Could be many things.
The only way to get the data back would be to get software that reads the drive surface and ignores the file system, or tries to reconstruct it (or pay for a service company that does the same thing).
Of course, you DO make regular backups, right?
Undelete is one software package. It's not specified whether it can recover an entire partition though. It looks like it only undeletes within a file system (a working one).
Also
Undelete, oddly the same product name. Also doesn't mention partitions.
Stellar Phoenix specifically mentions accidental formats. You have to buy it specifically for the file systems you use apparently.
VirtualLab is similar.