SERIOUS startup problems

After hitting the power button, this happens; white screen with apple logo and spinning monochrome dial (normal), THEN it seems to only flash a hint of the boot panel, then jump immediately to the blue screen without any login screen or anything. It stays on this screen infinitum.
I've tried everything I know (albeit not much, but still). reset the PRAM (3x),
restarted in safe mode, single user mode, superfly snukka mode (I EVEN RESET THE CUDA BUTTON!!!) nothing.
I even managed to cram the install disk in it to use Disk Utility, and ran THAT! But once restarted, it picked up it's old bad habit again. PLEASE help,
please!

Reinitilize it and reinstall. ya it takes a few hours, but that will be a fix.........

Yeah, that was my last resort, and I did that. Everything seems to be fine. But I'd like to know the source of the problem. If anyone can help, I'd appreciate it.