Connection failed SQL Server 2008 R2 with Instance Name but with IP connect

Hello,

We have a server where SQL Server 2008 R2 is installed. Now from our local pc we connect to that database. I try to connect that database using instance name but cannot. If I put IP Address in the server name field, then it connect. my other colleague, they can connect using instance name but I cannot.

How can I resolve this problem? How can I connect using Instance Name?

Please help.