hey, i got the same error once, its kinda annoying. But all i could do was to , uninstall and install SQl Server back again, You can get the back-up of your databases from

C:\ProgramFiles\MicrosoftSQLServer\MSSQL.1\MSSQL\Backup\your_database_name.bak

And also note that, C: could vary to D:, E: or watever, depending on wat your active partition is. But mostly, it is the C:

Just restore the database back again once you have re-installed SQL .