The pulsing blue light on the power button is an indicator of battery level. The more “on” the the pulsing is, the more charged your Onewheel is. If the LED is mainly off with brief pulses of “on”, then your Onewheel is low on charge. When this happens you will want to turn your board off and charge it.
If the power light is blinking and not pulsing, your board is relaying an error message. You can refer to your manual for a list of error messages but generally you can power the board off and back on to continue riding. Make sure your Onewheel is placed on the ground when you power it on and that there is nothing engaging the pressure pads – these are some of the most common occurrences that will trigger an error message.