[OT] Problem with Asus K7V

Hi List, I have just broken the motherboard of my PC, so I installed an Asus K7V slot A on my machine. Everything works properly, but the MB can only see half ram. I have two DIMMS of 256mbyte, it reconizes them just like if they were 128. I have seen this when I try to remove one of the ram slots. What could be the problem? I have read the whole asus manual, but I cant find anything about it. Solution and advices arevery welcome! Praise