Mostly the android problems comes when the device is running custom ROM, or may be some time software issues. if you are trying to device into download mode or factory reset (Recovery Mode) but all the keys not working even the keys are OK.[br]
so first you can reboot device into recovery or download mode using Z3x Samsung software Flashing Tool. (Just connect device and from z3x reboot into recovery/download mode)
second if you have not Z3x Box then simply Download SamFirm Tool(Link: https://samfirms.com/samfirm-tool) which is totally free, a window based application connect samsung device and from SamFirm Tool press Download/Recovery Mode.
after that flash Stock ROM by downloading from: https://samfirms.com/