Welcome to the Se7enforums! reynajoh
Antman summed that one right up fast there!
When using a tv tuner card or some multimedia player in 7 the Aero theme reverts to Basic as long as the application for something like a tuner, capture card or media player is running in order to conserve on resources since some media players as well as the media played or even videos captured will draw more heavily on system resources.
It looks alarming and odd at first but you'll get used to it fast and nothing to worry about.