uhm ive got a problem with maya. When im busy with modelling everything is fine but after 20/30min my maya is going VERY slow and i need to wait 10 sec before it does something and after 1 min getting it so slow my screen fall out so i get black screen en my monitor getting on stand by. i think its my memory but i wanna be sure what it is.

can some1 tell me the problem?

system:
Processor pentium 4 2.4GHZ
memory 512mb ddr
video card ati 9500 series
Hdd 1x120GB and 1x40GB