what is the 120a fuse for that in my engine compartment?

THE SYSTEM IT RUNS SHOULD BE ON THE LID. 120 AMP FUSE SHOULD BE A MAIN PWR FUSE

That is the main fuse. If the car starts it should be Ok, but needs to be replaced if the cover is broken. I hope you really didn't replace all those parts before checking here... Nissans have problem fuel pump relays and a few other things that need special tools for diagnosis. Basic fix not easy to give this way, need to see it...