winfast ram problem

[Explosivo]

hi

i'v just built myself a new pc using a winfast NF4SK8AA motherboard

the problem i have is if i put more than 2gb (2x1gb sticks) the thing gets to the windows boot screen then just keeps restarting

i'm using ddr 400
it says in the board manual that it supports up to 4gb ddr400

all sticks are the same 1gb corsair sticks

it's with a athlon x2 4400+ & an 8800 gts 640mb (incase that matters)

any ideas whats wrong?

thanks