I asume you meant you unplugged the phone and not the battery. If that is the case do this:
Check for liquid damage: http://support.apple.com/kb/HT3302
Put down your phone flat on the table and look at it from the side. Is it still flat or dies the front or back glass bulge? If it is flat proceed otherwise you'll need repair.
Plug in the phone until it starts getting warm and then reset the iPhone by pressing and holding the sleep/wake and home buttons and releasing them, when the Apple logo appears on the display.
After that see if the phone still gets warmer while charging.
If it does and it does not power on anymore you'll need to have your phone repaired.
If it does power on and only heats up slowly you can try to restore.
TAKE CARE NOT TO RISK DAMAGE TO PERSON OR PROPERTY!