Hmm... Roxygotchi is right but your tamagotchi's screen might of exploded or it might be on "Lights off" and it froze because water got into the screen! Hope we helped!
during the summer i left mine in the car and the screen was black but the tama was still alive i just help it in front of the air conditioner and it cleared up if its cold out you can also try the heating it up thing but not to lon g though Good Luck