Mine is doing this as well on a Dell laptop with an Intel video card... screen flashes (with very brief audio blip) then screen freezes with screen-filling blue box. I too have to tell LMCE to stop the process to get control of the media director. Odd thing is that my Acer Revo has no such problems- tv plays just fine.
I will add, clicking on "TV" at the top of media allows me to watch TV just fine. I am unable to watch through my cable box which is setup as the 2nd (or 3rd) option in the media. Not sure I"m being clear- clicking to watch TV by clicking on "TV" from "Media" works just fine, but clicking to watch TV through my cable box causes mythtv to freeze. All of the signal, regardless on how I watch tv, is piped from a single PVR-150 on the core- nothing is installed on these MDs.
Other than the physical location and the MD hardware, these MDs are essentially identical. I mean that the peripheral equipment installed (for each only a gyration remote is installed) is the same- no USBUIRTs, external amps over RS232, etc.
I am running a 810 install from June (ish) time frame if I were to guess... updated everything via apt-get update && apt-get upgrade on the core and MDs. I have not see if the 810 LMCE release DVD solves this. I would guess I have had this issue for a month or so.