mplayer on a dual head setup

Hi everyone. I've a laptop I've which I dual head at home with an lcd monitor. It works fine apart from videos (of any type). The laptop alone plays them fine but I can't see them on the lcd dual screen under M-player. the strange thing is that Avidemux plays them no problem at all. Under M-player I get sound but a blank blue video screen. The lcd plays them fine too when connected directly to the server. 10.1 There's some stuff on google but not quite what I'm describing. Any ideas anyone? Cheers, Steve.