Hi Sebastian,
Do you have NI VISA installed? If not you can find the latest version
here. After this, you should be able to expand the Devices and Interfaces tab and at least see your built in COM ports on your computer. If you have VISA but cannot see anything in MAX, you might want to try either installing the latest version of the driver, or repairing the VISA installation or MAX.
Also, do the COM ports show up in Windows Device Manager?
Thanks,
Adam W
Applications Engineering