Motopsychojdn, just because a CPU is AM3 does not necessarily mean that the motherboard socket is AM3. I have an Athlon II 620, an AM3 chip, which is running in an AM2+ motherboard with no problems.
Unfortunately for the OP, I do not know what the socket is on the motherboard. If you open the case and find a model number on the motherboard (usually between PCI / PCIe slots, at least in my experience), this should help. Search for that board, and it will tell you.