the problem could lie elsewhere. make sure all projectors and playback are run on the same power. otherwise you can find voltage coming down the screen on the video cables. this will lock up your computer no problem. I always run mains power out to the projectors from the playback position to avoid ...
I think you'll find modul8 is currently more suited to live performance than time-line based work.
try vjforums. there was a similar subject there recently.
the amount of VRAM and RAM you have will have a big effect on playback ( too much is always better than not enough) as will the number of active layers you have up in M8. try deinterlaced PAL video with either H264 or photojpeg codecs. if you use a MIDI controller you can have a back-up mac running ...
keep the number of layers being used down - I only use 3 layers for my shows.
and try not to use massive movies - using the right codec helps too.
I'd try photojpeg or H264