@sinned6915 here are some possible causes:
Shorted heater, or short between heater +ve wire and ground
Blown (short circuit) stepper driver
Blown (short circuit) 5V regulator
I suggest you inspect the stepper drivers and the 5V regulator U3 for signs of damage. If there are none, then disconnect all heaters and stepper motors from the Duet, replace the 7.5A fuse, and apply power again. If the fuse fails again, the problem is on the board. If not, then it's probably a heater.