Why will my NObreath not switch on after charging?

My NObreath device is not turning on after being put on charge

NObreath-turned-off

In firmware version V4.07, a muted charge mode was added. If the device battery is completely
depleted, connect the device via the USB to the charger and then the device will enter a muted charge mode.
In this state of charging, the device will not emit a beep or display any charging animation on the
screen for up to 90 minutes while the battery is in the recovery process. After this duration, the beep and battery charging animation will resume on the screen as usual until the battery is fully charged.
If the problem persists or has not been resolved by the information provided above, please contact Bedfont or your local distributor for more advice.