Sorry for asking the bloody obvious, but has tempdb been deleted? As you cannot start the SQL Server service, check in Windows Explorer for existence of C:\Program Files\Microsoft SQL Server\MSSQL\Data\tempdb.mdf (well, this is the default path anyway). Or does the full error message suggest that SQL Server cannot find a certain system table within tempdb?
As you cannot reboot a database, I assume you mean the server itself - is that because it hangs?
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.