Yesterday at the end of a walk my Spark 3 displayed an battery symbol on the screen with a line through it. Since then the screen has gone blank. Have connected it to charge but computer does not make usual sound on connection. After "charging" over night no difference. Pressing down button to reset the device brings up the clasped hands symbol (so there is charge) but nothing further happens and symbol disappears. No reaction from any other button or combination of pressings. Any suggestions or is it dead?