why i can't start my gdm?

tux

i configurate rc.conf and make the gdm as default dispaymanager,still
and init level changed to 5,but still i can't see gdm  as booting ,
i have to manually type gdm or type startx then i can enter X ,
MAY Somebody tell me why and how ?

cmxxz

rc-update add xdm default

tux

it's ok now thank you ever so much !

realtang

晕，用xdm登陆。