Default +Can I replace the bootloader with fastbot

I have a samsung Galaxy Nexus I51i Verizon. Two problems, ADB doesn't see it, and the bootloader is corrupt(?). With the bootloader booted ADB does not recognize that the samsung is there, but fastboot does. IF I try and put the bootloader in recovery mode, I get a belly up Android with a red triangle and exclamation mark. I'm thinking replace the bootloader using fastboot but don't know the commands.

Larry