Check the SQL Server log and the Application Event Log on the server wehere SQL Server resides. See if it had trouble binding to the TCP port. If it did, you'll see a bind error. If there is one, run a netstat -an and see if there is anything listening on that port. If there is, you'll have to track down what it is and stop it. If there's not, stop and restart SQL Server.
K. Brian Kelley
@kbriankelley