Easy solution.... Download the firmware from sammobile for your device by model number, download Odin. Then power off the phone, hold volume down, home and power at the same time. Press volume up at the custom OS warning.
Plug the tablet in open Odin choose PDA or AP depending on the Odin version you're using. Choose the firmware you downloaded.
Press start and it will reboot like new.
Note: This will do a data wipe on your device. Backup anything important prior to doing this.