Sounds strange. Do you have the bracket locked into the correct place suitable for AM3 mobos? Is the backing plate around the right way? See this video. He's a bit rough, but it shows where it all goes:http://www.youtube.com/watch?v=hSq_xbxsm7Q
Ah, Perfect! Can't believe I had it so backwards - well I can, but...
Thanks for the link!