Dell laptop

unplug it, pull the battery out and push the power button down for a couple of seconds, and then put the battery back in and see if it powers up.
 
what's the dell Service Tag? we need a lot more information to help you... like how old is it? how old is the battery? do you have the battery plugged in when trying to start it? do you have the power plugged in when trying to start it? does it start without the battery but power plugged in?