can't use both memory sticks at once.

[baison]

hello TPU , i have encountered a strange problem tonight while building a PC for my brother ..

CPU : intel C2D 2160
MB : P4M900T-M
PSU : 450 i think but he does not use any grafix cards just the built-in one with the motherboard


the problem is he bought 2 1GB PC2-5300 memory sticks and when we use them both on the 2 dimms in the MB system will boot only with 1GB memory , i tried to boot with each stick on every slots and both memory sticks and slots work just fine , but together system read them only 1GB , now the crazy part is when i use them both and check with CPUZ it shows both memory installed >< another weird thing is when i unplug 1 stick and use 512MB PC-4300 on any slot system read total memory 1.5GB ..... i tried to increse the voltage from the bios ,flashed the bios with latest version and nothing seems to work ,,,, any tips guys ???


thanks in advance