Because: - your CPU is overheating - your graphical card is overheating - your power supply is too weak - and some other possible causes taht I do not know...
Presario ? That's a mobile computer, right ? I suppose the fans are running full speed while you play, aren't they ?
It might be the CPU can't handle the sim, because it's a 64 bit which means it runs at a slower speed but it can handle twice the information, I would try turning down the settings, and if you haven't gotten SP1 download it, also try to install more fans inside the case if possible
Could certainly be all of the above - and/or the Out of Memory problem. There is a thread with a fix in this forum (by Miltestpilot). But it sure sounds like you need to check your hardware and power source.