What version of SQL Server? Is this an Express version? If so, it's probably just not started. You'll have to locate it within the file system to get it started. If another version, it sounds like either the server is shut down (look in services on that machine to see if you can start it, same can work for the Express version) or you don't have permissions to it.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning