If you’re getting absolutely no response from the device, the most common answer would be that the batteries are dead. You can access the batteries by unscrewing the back panel of the device. If the batteries are not dead, then the problem must with the internal components of the device.
This could also be due to bad connection of the wiring that gives power to the device from the batteries. The wires might be severed or detached from their terminals. Check out this troubleshooting page for more information.
One last reason for the device not responding could be due to water damage to its critical components. This does not means that the device had to be completely submerged in a pool for water damage to occur, but this could have also happened if the device was left in a humid setting, in mist, etc. There are some remedies that might be of use if the device was not completely submerged that can be found here.