Try to access Dell's Data safe recovery.
Windows key plus 'C'
Settings/Power
Hold down 'Shift' key and select 'Restart'
Then it's Troubleshoot and Advanced Options
Windows will try to 'Repair' your System and will eventually lead you back to Advanced Options, where one of the Options will hopefully be Dell Datasafe.
If this is unsuccessful, or you can't run Windows, and if you didn't back up Windows 8, then you'll have to buy Recovery Media from Dell...