Maybe the magnetic heads have been dried, or the printer doesn't have enough ink to print, or there's a problem with the drivers. I would start to reinstall de drivers and if this doesn't fix the problem, I would look the heads.
Could be a problem with the lcd screen or maybe a problem with the graphics card that is integrated with the motherboard. I would try to connect the imac to an external monitor if the image of the second monitor is ok u can reject a problem from the motherboard and look if it's a problem of the lcd screen
Posiblemente algún componente de la placa se haya dañado y esté creando una resistencia que hace que el iphone se caliente, si tienes un tester intenta mirar los voltajes para ver si está todo bien. Aunque cuando un iphone se moja es dificil de recuperar