Socket A and Socket AM2 boards aren't compatible
The Asus A7N8X was designed for use with AMD's older "Socket A" line of chips. It isn't compatible with newer socket types like the AM2. Attempting to use an AM2 chip with the mainboard could damage the mainboard, the chip, or both.
Specifications
The A7N8X, released in 2002, is designed for use with CPUs in AMD's Athlon XP, Sempron and Duron line. It can support anything in those lines, up to the Athlon XP 3200 --- multi-core processors weren't designed for use with Socket A chips and are not supported by the A7N8X. The A7N8X is also limited to RAM and CPUs with a front side bus ("FSB") clock speed at or below 400 MHz.
AMD Socket Types
Sockets designed around the specifications of AMD are generally "pin grid array," meaning that the CPU has pins that are designed to fit into small holes in the motherboard. This is in contrast to "land grid array" (LGA) chips used by Intel, in which the CPU doesn't have any pins and simply sits in the motherboard's socket.
AM2 History
Socket AM2 was developed in 2006, about four years after the A7N8X mainboard was released. It followed the Socket 939 platform, so called because the CPUs had 939 pins --- around twice as many as the 462 pins in a Socket A CPU, which are the CPUs designed for use in the A7N8X. Because of the wide difference in the number of pins, a Socket AM2 CPU won't even fit in the A7N8X.
Tags: designed with, grid array, pins Socket