I'm not 100% sure, but it sounds like your com.apple.Boot.plist file is somehow messed up.
you will find it at:
In it make sure there is no line that reads something like:
If there is no Graphics Mode statement in this XML cascade, it should default to what the computer has.
If not, you may want to change it to what you have
and see if that works.
(oh, and you probably want to do a repair permissions before you reboot … if the system can't read this file on boot, it won't boot.)