I just got through with this exact problem with the FX 8320 and it was extremely frustrating. I honestly don't think they can expect you to put as much force on the mobo as it would require to get both latches on normally. I had to loosen three of the four heat sink support screws (the piece that comes mounted onto the motherboard that the heat sink's brass tubes rest on, or at least they do on mine, the ASUS M5A97) to the point of almost coming out, and only then could I manage to get both latches on and flip the lever. (which I did very gradually and with steady force)