Neither radio will receive or send

Motorola Talkabouts usually a have a CODE you can set for each channel. This is like a TPL / DPL code. If its not set the same for both radios then other radio may not receive.

GP300. Assuming they are programmed to talk to each other, ie RX and TX of each on the same frequency or they may talk through a repeater and that the TP/ DPL code are correct. If you have the Speaker icon crossed through they are probably muted, but in this case you should be able to unmute them from the keypad. Only other thing is if they are programmed for Selective Call, then they would only unmute on a call which contains their ID #. There several Selective call systems, MDC, Select V , Quick call are just some. Europe usually opts for a certain type of Select V. US uses MDC.