I had a system using a Phenom II X4 (940 I believe but not quite sure) on an AM2 class motherboard Gigabyte MA790X-UDP4.
The motherboard got fried.
I did a little shopping around and found the ASRock 970 Extreme 3 which has support for AM3 processors and lists the Phenom II X4 as being supported.
When I try to insert the CPU in the socket, I feel that the pins align but the CPU doesn't drop in the socket. I have carefully applied a small amount of pressure on the CPU to "encourage" it to drop in but, to no avail.
Can someone confirm for me that the Phenom II which was originally installed in an AM2 socket can be installed in an AM3 socket ?