What would be causing my 2002 Arctic cat 500 4x4 ATV to over heat?

The radiator was pretty dirty I blew the fins out with a compressor and it looks like new. I also put a new fan in. All the connections look good. Is their a relay or something that could trigger it to over heat. The fan does not come on when it overheats. I also put a new water pump and thermostat in. So what else could it be? Wheres the part located, and about how much to fix myself? Thanks|||if your fan is not coming on then there you go. fuse,relay of the fan itself is no good|||It's on heat waiting for you!