Why it is not starting?

means dead short in the wiring to the starter or a bad starter relay shorting out

Sorry if didn't help brb I a check something that can probs help

u need to check that the battery was installed correctly. red cable to positive and black cable to negative post. did u get the same size battery as the old one?

Try a slow blow fuse? I think thats what they are called.

You have a short. you will need patience to route the wires from the harness to the light source, and to inspect for frail damaged wires.

hi,i would say the solenoid on your starter is faulty

It sounds like that fuse is supplying power to more than just the amp and is being shorted out in the START mode. Normally I would think the power to the sound system would be cut off by the ignition switch in the START mode. Try to find out what else that fuse supplies power to. You can disconnect suspected trouble areas to see if that helps locate the source of the fault.

There is a major electrical fault that keeps blowing the fuse. The fuse protects that part of the electrical circuit, 40 amps is heavy electrical circuit, it it wasn't protected by a fuse it car could catch on fire.
You need to get an auto electrician or your Mitsubishi service center to locate the fault and repair.
If you had a wiring diagram for your car then you can trace the wiring from the 40A fuse to the various components to locate the wiring fault or component fault.

REMOVE FUEL PUMP RELAY.REPLACE FUSE IF STILL BLOWS SHORT IN PCM TO IGNITION CIRCUIT.IF FUSE DONT BLOW I AM LOOKING AT A BAD FUEL PUMP RELAY OR FAULTY FUEL PUMP.

Your fuel pump is internally binding and causing the fuse to blow. Change the pump (and filter while you're back there.)