Hi there,
don't know what DM is on as I found your Mobo without any real problems. Most probably not relevant at the moment but which revision No. is it?
The AM3 CPU's are normally pretty easy to fit, as you say, line up the corect corner and drop it in. However, when you remove a CPU from a Mobo it is possible to accidentally bend 1 or 2 of the pins. (I know, because I have done this myself) This can stop the CPU from dropping in cleanly when you offer it up to the socket again. And, the pins do not have to be badly out of alignment to cause a problem either.