1998 Ranger wont start.Help please

Ok all you electrically inclined ford people I need your help I do not know where to go from here. I am writing this for my husband he is mechanically inclined and I am a computer geek.
1998 Ford Ranger XLT Will turn over but will not start. I was on vacation 3 weeks ago left my ranger parked in my driveway while I was gone the factory installed alarm went off I told roomate to use the old door remotes to shut it off. I got home truck would not start jumped it and it started went to store after driving around and it would not start again jumped it again and it started took the battery in was told it had a dead cell replaced battery drove for a few days, the alarm went off again sitting in driveway, would not start again and would not start with jump replaced starter problem fixed for 2 days. On the way home from work truck dies just from taking off from light had to get towed home 30 miles. So far I have now replaced the battery, starter, fuel pump, cam and crankshaft sensors and have checked the reset relay power is getting to the fuel gages but not the fuel pump. This truck has a factory alarm and an after market auto start. The keys that are the originals however look like duplicates since they are the not big ones that have the chip in them. My sister was the original owner of this truck and the keys I have are the originals that she got from the dealer. All of the relays and fuses have been tested that I can think of. Oh yeah the original factory alarm is hooked into the auto start this was done about 4 years ago. The engine is 6 cylinder 3.0 automatic. Can anyone help me besides taking it to the ford dealer which after the 800.00 in parts I now cannot afford? Any idea? Clues? What have I missed.
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penney wrote:

Now is your chance to help him become computer literate!

Why did you replace the starter, fuel pump, cam and crank sensors?
I think you found an important symptom: No power at the fuel pump. Unless it is a mechanical fuel pump, it will not work without power.

Well, one important $800 lesson is "Don't fix things unless you know what is wrong first."
I am not trying to come down on you or anything. Unfortunately, a lot of times people seem to just fix anything that might be causing a problem rather than finding out what is really wrong.
I have no idea what causes the power to the fuel pump to go on. There my be a relay that is controlled by the alarm. The alarm appears to have tripped. This might be part of the problem.
The other thing that I wonder is how is your alternator? If your alternator is bad, this can ruin your battery. And if the voltage in the battery drops too low, this might trigger the alarm. Just a guess. But, you need to check out what can be wrong, in a systematic manner, and then figure out what is really wrong.
Jeff
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