No valid dongle

When I try to start the software I get the message ‘No valid software protection key (dongle) found!’. Why?

Our software packages are protected by so-called dongles. A dongle is a small USB device (looks like a memory stick) which must be present in one of the USB ports of the PC in order to run the software. If you get this message the dongle has not been detected – very likely it is really not there.