I understand you are having problems with the Abit AV8 motherboard paired with the AMD 64 3400+ cpu, well, for one obvious problem I see is the motherboard and cpu mismatch.
The Abit AV8 motherboard is a 939 socket, the AMD 3400+ is a 754 socket, while the cpu may fit on the mobo you won't be able to use the dual channel memory feature and I suspect the mismatch would cause other problems as well. TigerDirect is also selling the motherboard combo and fail to mention the socket for the cpu. One would assume the cpu is also a 939 pin but it isn't. the dual channel memory PC3200 latency and voltage must also match your mobo.. I am searching the internet for a good 939 mobo, and Abit AV8 and the Asus A8V get high marks. hope this helps some Gary