First look in the BIOS, can you see your drive there ?
Run a Full scan with Repair:
Start > All Programs > Accessories
Right click on Command Prompt > choose Run As Administrator
Type: chkdsk /r and then hit enter (This is providing there is only one disk and it is the one with the OS on it)
You will get a warning and you will be asked to run diskcheck at the next startup > say yes.
Restart the computer
Do not interrupt the process.
Or here is data recovery software : http://www.cgsecurity.org/wiki/PhotoRec