it could be a leak where if your segment or wall entity somehow is not solid the computer will then calculate everything in the entire build area.
i found this out with the dungeon pack as soon as i got to a certain doorway area it froze to one frame a year, and i have quad core etc windows score of 7.0. so i got around this by encasing the faulty area with good solid segments, so the level is the same but in construction mode you create a bubble around the area.
also do you have xdriver 10.1 and update v109. both rely on each other try these before spending on a motherboard. plus you prob need 8800 series graphics card just go to top of the forum it gives the specs there.
an unquenchable thirst for knowledge of game creation!!!