In most cases when this happens the Konftel Ego is in upgrade mode and have an arrow on the display. 
That arrow indicates that your Konftel EGO is set to Upgrade mode.

To get rid of the arrow, you can connect the USB cable to your PC and upgrade the software.


Press and release Bluetooth - Mute - Bluetooth  - Mute - Bluetooth  - Mute - Bluetooth  ....until the arrow disappears. 
The trick, with the key combination, is to make it in slow speed

You can now start the unit on the power button.