The first thing to check is the battery. Connect the instrument to a power source via the USB cable. A computer, or the supplied mains>USB converter will both work. Leave the instrument for 30s, and then try to power up again.
If the instrument beeps but the screen does not turn on, this indicates that there is an issue with the screen. This will require repair at a Rhopoint accredited service centre.
If the LED lights at the base of the instrument turn on when the power button is held, then the instrument is in programming mode. This will require repair at an accredited service centre.