From the SQL Server Configuration Manager:
1. Make sure that the TCP/IP protocol is enabled.
2. In the properties of the RCP/IP protocol, ensure that the IP address that clients are connecting to is “Enabled” and “Active”
3. Ensure that IPALL settings are 0 and 1433.
4. Ensure the following rules are setup in Windows Firewall:
Outbound TCP 1433-1434: Allow
Outbound TCP 1433-1434: Allow
Inbound UDP 1433-1434: Allow
Inbound UDP 1433-1434: Allow