You have to do some diagnostics and post results unless you want to just get guessing answers.

on the db server in command prompt do:

telnet localhost 1433

do you get connected, or a "Could not open connection to the host" error?

then on your workstation do:

telnet --servername--1433

get connected?

you can also do a "netstat -a" and look for

TCP servername:ms-sql-s ... LISTENING