Welcome to Android Central! If there isn't a Reboot option, then force a shutdown by pressing and holding Power for 10-15 seconds. Then power on normally. If it keeps going to Fastboot, it's possible that one of the volume buttons is stuck in a pressed state--so when you try to power on with the Power button, it thinks you're pressing Power and Vol Up or Down together (which might be the button press combination to get to Fastboot). If that's the case, you'll have to go to a repair shop to fix the button.