The digitizer is under the screen - it detects your touch, sadly, it is damaged by heat. If it were working at all you might be able to compensate via adjustments in the settings if it's not working at all the screen and digitizer will likely need to be replaced. Although the screen may be fine it's glued to the digitizer which is very fragile making it virtually impossible to replace separately. With care you can do it yourself or take it to a shop.