There are many things that could be the cause of your problem. Three possibilities are:
Have you got LM_LICENSE_FILE set correctly? if your license server has moved (to this machine) are you sure you are not still looking for a different server. If you have the pcls_ok utility, use it to check where you are looking for licenses. If you have an old reference, correct it.
Do you need a license server? Only if your license includes a SERVER line and the INCREMENT lines have a count of 1 or more. (If your license has a count of 0, then no SERVER line is required. Instructions on setting up a license server are available here.
Is the only change that the machine is now out of the network? (The license server has always been running on this machine, but it has now stopped working.) Disconnecting the Ethernet cable used to cause the network card to stop. This used to cause problems with licenses based on the MacAddress, but I've not seen problems specifically with dongles. This can be overcome by setting the registry key as detailed here.