Bronco won't turn over

Hello, here's the problem

The bronco will rev up but never turn over.

87 Ford Bronco with fuel injection system

Some history

This Bronco is fuel injection and had been sitting for awhile(3months+)the battery was still good as we did go out and start it up now and then. Last week my brother went out to start up the vehicle to back it up a few feet and he did so only to have the vehicle die on him, not caring or too rushed at the time he didn't bother to try and start again he simply got out and left the vehicle for the time being.

Until annd couple days ago when he attempted to start it again and he ran into the problem mentioned above, the vehicle won't turn over, my brother and I speculated that someone might have siphoned the gas out of the tank while it was down. Since trying to start it up again we've put about 2 1/2 gallons into the Bronco but it still won't turn over, our Dad thinks that the fuel pump might have failed, I don't have a clue what the problem could be.

If the vehicle had run out of gas and is fuel injection would putting a couple gallons in it get the vehicle working again?

The vehicle prior to all this worked fine and started like a champ all the time.

Any help is appreciated, thanks!

i know i have an 85 bronco, and my fuel pump went out when it set up for about 9 months. It was out of fuel, and the rubber boots and whatever else is in there deteriorated. What do u mean rev up? i thought u said it wouldnt crank? Is the motor turning, just not cranking, or what? Could be some vacuum hoses were eaten through by mice. Test to see if your getting spark and gas. Narrow it down some.

sorry when I say rev I mean the sound the engine makes when it's starting up or rather(in this case) when it's trying to start up. If I hold the ignition key in the start position it will continue to try and start until the battery starts to loose power in which case it starts to slow down, we had to hook up jumper cables to continue trying to start it but nothing has worked.

I'll look into your suggestions and post and update.

Thanks!

Curious what would a reasonable cost for a fuel pump replacement for this vehicle?

it also may be your starter (that was the case with mine, it was getting gas and fire, and just kept turning. I replaced fuel pump because it was leaking gas into oil) Your fuel pump is mounted on the rail somewhere (where mine was mechanical, and it was $15) check autozone.com, or advance autos, or oreilly auto parts if you have one where u live. It shouldnt be too much though. Unless you need a high performance one, if your motor is stock, your fine. Only need high performance if youve changed major stuff.