Blender crashing...

Sorry if somebody has already answered this question, i wouldnt be surprised, but i looked for it everywhere and couldnt find anything.

Recently i have noticed that when a scene is rendered, if it has more than (about) 100000 particles in it then the render just crashes. there is processor activity but it just sits there, with a blank render screen (not even the gray bar at teh top of the render screen was there). when i brought this number down to about 50000 particles, it rendered fine, the gray bar at the top was there from the start. Its not as if its just taking a long time to render though, i left it for quite a while and it was still in the same state (i have no doubt that it has something to do with the memory though). After attempting to rendering a few times with different amounts of particles i found out that the threshold (i havent spelt that right have i) seems to be around about 70000. however just today that number jumped down to about 20000, adn now i cant render my scene. Has anybody else had this problem, and knows how to fix it?