Soyo P4I 845PE lite overclocking

hello every one I seem to have a problem for some reason I caint raise my vcore at all even by the smallest amount if I do the computer will not boot. Here is my system
P4I 845PE lite MB
P4 2.4 533mhz
PC2100DDR
ATI9800pro
Soundblaster live 5.1

So I want to no how to fix this thanks.