How to fix my tablet .., it reboot on "samsung galaxy 10.1"

one day i have experiencing many ads after i open my tablet then after next week my tablet is rebooting until only on logo which is "samsung galaxy 10.1" and then until now i cannot open my tablet. i tried to reset it by hard reset but it will reboot again and again until the battery is not lowbat. also i encountered this "Warning!! A custom OS can cause critical problems"