First the obvious of recharge it fully not just plug it in and try it.
Second - Depending on the make you can jump start them if it was due to a crash but how depends on the manufacturer. It may be just hold the power button for some length of time or multiple buttons. See the manufacturers website.
Third - the battery may be dead and recharging it won't do any good so the battery needs to be replaced. Apple products means you have to send it in or go to a repair facility.
Fourth - If it was someplace hot or col then it may have to get back to room temperature.