Asrock K7S41/K7S41GX problem

I have a very frustrating problem with the above mainboards - put a system
together in usual fashion - have built several machines now, this is first
AMD system though - no boot - 3 beeps - checked beep codes = mem read/write
error. Cutting a long story shorter, I now have replaced board, chip,
memory, and run all combinations of original and replacement items. Jumpers
are correct for FSB vs. chip speed vs.memory. Drives plugged and unplugged,
monitor the same, keyboard and mouse also. Even tried power supply from
another machine. Still always those 3 beeps. There must be something
fundamental I've missed surely. Anyone come across a similar issue.
Thanks in advance.
Chandla