Graphics card help

hi my radeon 9600xt 256mb graphics card is running just fine
but its suppost 2 run even better.
its a 8x agp
my mother board can only handle 4x agp ok fine
i dont need the highest setting but my agp right now is 2x because
if i change it to 4x my computer display will be all messed up and it wont
even work all it is are white and black lines at bootup

any ideas?