I don't really know what the fans called but its the one under the power supply. Its not the CPU fan because that one works perfectly. Also the PSU fan works perfectly too. Its the one that lets all the heat out.

I installed the E8400 CPU a week ago. And the fan under the cpu stooped working. I'm not really sure if that's the problem. Its used to have a 2.0ghz i don't know what model. But here's whats weird when i turn it on you can here it work for about 5sec then it stops, When i put it to sleep mode and wake it up it starts working perfectly and doesn't turn off until i turn off my pc. I have to put my pc to sleep every time i turn it on. Is there anyway i can fix this? The fan that im talking about is a 3pin. Should i replace it? I'm not sure if its the CPU that i installed or if it even worked at all. I got this pc off Craigslist btw. Without the fan my cpu can get really hot and i don't want that to happen. Please help, i listed my specs in the bottom.

Specs:
Dell Vostro 200
Intel Core 2 Duo E8400 3.0Ghz

4gb Ram
200gb and a 1tb
GeForce GT 640