external monitor through firewire shows... nothing

After a crahs with FCP I had to re-install FCP and now my external monitor displays nothing when I play a clip. (The clip plays correctly on my canvas etc.)
My camera is reconized, I can capture my clips, but I cannot get the images shown on the monitor. I tried different dv in-out camera's and a DATAvideo DAC-100, but nothing.

Thanks in advance!