Wierd one, MyTrailers suddenly stopped displaying video but played sound ok. After various messings about I established that WMP wouldn't play the video either, all other videos played normally in MyVideos and MyTV. I sat and had a think when was the last time I had used MyTrailers and what had I done since then. BINGO! New video card and some driver shenanigans. Checked the configuration of the video card and the TV was selected as the secondary monitor, changed it to primary monitor and MyTrailers works again. The fact that all my other videos worked kinda threw me on this, for some reason streaming wmv wont display on this configuration if the TV is secondary monitor.