Was the project deleted from your disk? If not (it shouldn't..),
just re add it to your solution. Chances are it is still in your solution folder
(You can easily open it via Visual studio).
If it was deleted from your HDD, this is where things starts to get tricky. Try restoring deleted data from your disk.
You will need a software to help you with this task (e.g. this one was randomly selected using a simple google search).
In case nothing of the above works you can take your HDD to a professional lab to restore the deleted data.
If it is just a small project, I wouldn't bother. If it is not, Shame on you for not using SCM ;0)
Good luck...
If nothing of the above works, I am sorry for your loss...