Named instance cannot be accessed from another computer after IP address changed

Hello

In our SQL server computer, we are using dynamic IP.  There are two instances; one of them is a named instance.

We can access both instances.

However, after changing the SQL server computer to static ip, we cannot access the named instance from another computer (the non-named instance is ok).  Any idea what to do to make the named instance accessible?  After the ip address changed, I only did a ipconfig /renew without rebooting the computer, would rebooting solve it?

Since I only have limited amount of time to take the production server offline and since I do not know enough about this, I ask to see if any one has any idea.

Thanks

Carbond