Sometimes when installing a FlexNet license server, it will not connect to the PTC server even with a proper license file - showing an "Unavailable" status (shown below). 

This can be caused by many reasons, but the best way to troubleshoot is to manually stop the Windows Service named "lmadmin_ptc" and uninstall FlexNet. When trying to uninstall FlexNet, you will get the following error:

If you receive this error regarding a missing DLL file, you have to install the Microsoft Visual Studio 2013 Runtime Libraries (x64), which can be downloaded here.

If you receive a similar error but because of MSVCP100.dll, you need to install Microsoft Visual C++ 2010 Redistributable Package, which can be downloaded here.

Other versions can be found on Microsoft's developer portal.

Once that installs, you can do a proper uninstall of the FlexNet application. 

The Windows service of lmadmin_ptc will likely still be running after the uninstall, so unless you do a restart of the server or computer you will need to manually delete this. Open up a command prompt and run sc delete lmadmin_ptc - this will manually delete the service.

Now, do a reinstall and setup of the FlexNet application for it to work!