Olympus Mju mini - lens

check out first if the battery is fully charged.and if the battery is very old.then prefer replacing the battery instead of charging.and if the battery is new,then the cover of the lens must be getting stuck up so try tapping the device from all the sides it will automatically get opened.also off the camera completely and try to move the lens door manually up and down.sometimes the gear assembly gets stucked and this makes it free to  move.