follow the above info and you'll be buying a new cpu. There is the larger fan in your power supply, and often a smaller one on the cpu itself (on a heat sink) on the logic board. They are there for a reason. the cooler the cpu, the more efficiently it operates. get it too hot and it will literally melt, particularly with the high clock speeds these days. the fan on your cpu should stay put. as for the other larger fan, it also helps cool your expansion cards and the logic board in general by creating airflow. most cases (if you have a generic PC case) are designed to produce front-to-back airflow like a windtunnel. removing the case or the main fan prevents this from happening. It also prevents the case from doing its job as ESD protection, as it is usually lined with metal to provide a kind of faraday shield from static and grape juice and stuff. that said, plenty of people run systems w/o cases (I know one guy who found his cat sleeping on his logic board while running and it still works). the main fan does have a purpose though. if it is removable, there's a good chance you could replace it with a cheap new one from an electronics store.