did you get a fan from ati ? and there is no snapping in it screw's in make sure cause there are 2 sets of screws on the fan, one set to hold it to the logo the other to screw into fixture, also make sure the wire nuts arent in the way
the link you showed of the sunpower shows 4 screws also, i have a spare fan myself from my sunpower sitting in front of me. did u buy the fixture new or used ?
The link I showed has 2 rubber fittings that holds the fan in place attached to the ATI plate, and 2 plastic fittings that clamps to the fixture itself. The screws are silver, not black. I have 2 ati sunpowers here as well, and both have rubber/plastic fittings.
Greg was able to help me place it in, and explained to me the difference in sunpower fans and PM fans. Your fixture must have had the rubber fittings replaced with screws which is an option people take once the original fittings accidentaly break.