in order for the Asus A7N8x series to accept the sempron series of CPUs, you need to update the bios to the latest version using the asusupdate utility, before you upgrade to the new sempron cpu.

problem is that unless the mobo came out of the box with the latest bios updated, you will need to RESET the CMOS settings using the jumpers next to the mobo's battery after upgrading the bios, in order for the sempron to work.

(Pull the power chord from psu, remove the battery, change the jumpers next to the battery from [1,2] to [2,3] and back to [1,2] positions, place battery and power lead back, turn on your pc, hit DEL to enter bios, change your FSB frequency to 166 and you're smiling )

hope that helps.