Could you be low on memory?
I had a blank screen a few times about a year ago on Warlords using my old machine with 1GB of memory. My current machine has 3GB and no problems with BTS (except the initial problem of getting it to work with Vista).
Sun Tzu Wu
I run 1.5GB RAM. This never happened before and I usually keep a firefox window running while I play, though the blank screen happens regardless. How would I check?