What is the model number of the old CPU?
The AM3+ Socket is only backwards compatible with the AM3 CPU's. It is NOT compatible with AM2 and AM2+ CPU's. Most likely, the Athlon that you have is not going to be compatible with that motherboard.
Look on CPU SUpport list found on the following web page to see if your CPU will work. If your CPU is NOT on it then don't try to use it. http://www.asrock.com/mb/overview.us.asp?Model=970%20Extreme4