Just a couple of things I'd like to add to Larry's recommendations:
1) Did you try clearing the CMOS? My friend encountered a problem like yours when he first assembled his K7S5A system and he cleared the CMOS to solve the problem. If you need instructions on how to do this, go to: http://forum.ocworkbench.com/ocwbcgi/ultimatebb.cgi?ubb=get_topic&f=4&t=002019
2) Make sure your video card and memory chips are all firmly seated in their respective sockets. I'd try removing and then re-inserting them to be sure they are fully in. This has been a problem for some people.
3) Your power supply could be a problem since this board is very picky about the quality of power. Use an AMD-recommended power supply with at least 300 watts capacity.
Finally, if all else fails, consider returning it to the dealer for a refund - this board works fine once it is confirmed to be a functionally ok board.