I have a mega pro wich was working fine until i modified an oled display, will talk about it in a different topic.
It was powered by a phone charger, 5V usb, and now it heats even without the display, arduino only, but it still works, until it overheats and shut off.
What are the chances of only the regulator being faulty?
What heats up?
Were you powering the barrel-jack from 5V? If so, the regulator could have been over-powered, but the fuse should have opened.
If 5V was applied to 5V board pin, the Q/A may require more dialog.