You should still be able to get into boot loader mode, yes? Hold down power and volume down buttons? Use the flash-all.bat in the factory image.
Did you flash anything? Kernels, Roms, mods etc? It won't go into a bootloop for no reason, unless you deleted the boot partition or something. Do a full wipe in recovery, reboot. If nothing, try flashing stock, or a different ROM in custom recovery.
Sent from my Nexus 7 using xda app-developers app
Nook Tablet 8GB