Is the project still in the Aperture Trash? Then you can restore it by selecting it in the Trash, ctrl-clicking it and selecting "Put Back" from the pop-up menu.
If you emptied the Trash, the project will be in the System Trash on your Desktop. Then move the project to the Desktop and reimport it to Aperture.
But if you already emptied the System Trash, you will have to restore the project from your backup.
If you do not even have a backup, you will need recovery software like "Disk Drill" to recover the image files from your hard drive. Then it is very important not to use your Mac for anything that might modify your disk contents, until you recovered your images.
Recover Files from Crashed Drive - Disk Drill: Download from: http://www.cleverfiles.com/