Hmm. If you had put the phone in rice, it might have fixed it. But you should NEVER use a hair dryer on any electronic device unless you know

•exactly where the battery is

•what you're doing

•where important sensitive components are (i. e. Logic board, LCD, etc)

Ged is probably right. You should replace the battery, but be careful- it is extremely difficult and you could hurt yourself trying to take it out. I'm not trying to be pessimistic, but it has happened to me and if a battery is ruptured, it can release poisonous gases.