Are you using a named instance or a default one?
Did you enabled a remote connection on that instance?
Right click on the server and in the Server Properties dialog under the Connections tab check the Allow remote connections to this server option
In the TCP/IP Properties -> IP Addresses -> IPAII:
For a named instance you should set set the TCP Dynamic Ports to blank and port 1434, for a default instance you use port 1433 (this is a default instance that SQL Server uses).
After this step you should restart the SQL Server service for changes to take effect.
In the Programs -> Administrative Tools -> Windows Firewall with Advanced Security select the Inbound rules and New Rule:
- For a default instance:
In the Protocols and Ports window:
Select the TCP option, and in the Specific local ports text box enter the 1433 port
- For a named instance:
Select the UDP option, and in the Specific local ports text box enter the 1434 port
Make sure that your SQL Browser is running if you use post 1434.
If you're trying to connect with an Windows Authentication you may also encounter an error that you're connecting to an untrusted domain.
Also it would be helpful if you'll give the exact error you're getting
Hope this helps