Seems either it's not set to be the primary graphical runlevel that starts X automatically, or number 5 is not the graphical runlevel you're looking for.
/etc/inittab explains all these runlevels (if I'm right a little above that initdefault line), so you should be able to see there which are "normal" gettys and which ones are graphical ones. Or just try
from 3 up to 4 (you tried 5 already; 1 and 6 are for rebooting/shutdown and 2 is single-user runlevel, usually). If one of those gives you the graphical runlevel, change that to be the default.
Another thing: was there ever a graphical-default runlevel, or was it console-only from the install? Servers often don't use graphical X server because it's basically a waste of resources, all tasks of administration can be done from the commandline, which is more resource saving. In this case you'll need to set one runlevel to be the graphical-defaulting one.
