Can only see the terrain

[mm_the_broker]

After the game has been running for a few hours suddenly everything on the game screen disappeared except for the actual map. I could see the terrain ie the grass the mountains etc but no units, resources or cities. I had to wait for about 5 mins before everything reappeared. Has happened a few times so far. And once the screen went entirely white. Had to reboot the computer.I have an intel p4 2.8 ghz with ht and 512 mb ddr sdram and a geforce4 grahis card with 64 mb's of memory. Anyone else seen this problem?