Brake system not working properly

Firstly the brake pedal is depressed down to the floor. We have tried to bleed air from the system until the bubbles stops coming out from the bleeding nipples. still the brake pedal depressed to the floor. We have also check the brake shoes for excessive wear and adjustment but all are in good stages. We have tried to remove air from the outlet of the master cylinder and find out that the pressure is very weak. We bought a new master cylinder and replaced the old with it. At the moment the brake pedal is very hard to depressed and very weak to stop the car while test driving it. We have also discovered that the ABS (ECU) fuse blown and keeps on blowing when replacing it with a new fuse. Fuse blown when just turning the ignition key on.
Thanks and looking forward to your kind advice.

Bio Tekiau
Republic of Kiribati