I am assuming you flashed back to stock manually?
You didn't finish the instructions on how to do it, or had improper instructions. Start fastboot and connect to your computer via USB, open command/terminal window in your fastboot/adb directory and enter the following command:
fastboot oem fb_mode_clear
Then after the OKAY response, reboot your phone and it should start the OS normally.
If that doesn't work, power off and then back on but don't press/hold any buttons after the vibrate from the power button confirming it is on, once the bootloader comes up send the following command and copy/paste the output here...
fastboot getvar all
But make sure to mask out the IMEI and serial numbers.