Flysky nb4 noble transmitter won't turn on. Battery is at full power. Was working fine all day then went to turn it on and wont power up.

This is such a Chrystal Ball question, I would love to use my Chrystal Ball but its answers are very unreliable.

If you are sure the battery has power and making contact with the transmitter and also there is no reaction when you connect it to a PC then just go and claim warranty.

Thread for the radio....FlySky Noble NB4

Details are missing if you really want help:

"Battery is at full power", what exactly does that mean? You referring to the internal battery or external battery? If internal, I assume you cracked open the radio and checked the voltage with a meter? If external, that won't matter in your case because the external battery does not directly power the radio.
Have you tried pressing the reset button hidden behind the grip insert if the internal battery is actually in good shape?

The times I have seen your same above issue, it turned out to be a dead internal battery. Worst case, you'll need a new main board.