Some kind of thermal material is usually required to make a proper contact with the CPU. In my case the heatsink has this below a section of tape on the bottom, which must be removed just before attaching. Align the heatsink onto the CPU, don't apply pressure or approach at an angle. Hook one side using the metal clip, then do the other side. Mine required a bit of pressure on the clip -- the AMD video says use a screwdriver to help get the second clip on, but again avoid pressure on the CPU. Finally attach the fan power connector to the motherboard (should be labelled).