tec ma-1400 cash register lights on but keys dont work?

If all of the arrows are lit, you need to replace the battery. If not, it is probably not the battery. Make sure you have enough paper. If paper rolls are low, it will lock keyboard. Also make sure you have logged on with your pin number. The battery is internal and should be replaced by a dealer. If the battery is bad, it will have lost all programming.
If you need a manual, try here-

https://the-checkout-tech.com/cashregisters.php

Registerman
April 2018

https://www.manualslib.com/manual/171969/Tec-Tec-Ma-1400.html

Fryyh
April 2018