1998 Ford Explorer XLT does not start

My 1998 Ford Explorer XLT does not start. I am trying to describe the problem as good as I can. But since I've got no idea about cars, my language might not be correct.

The first time I tried it was with a jumpstarter to start it, yet no good. Something under the hood makes crazy clicking sounds time to time once it's connected to the jumpstarter, even without me plugging in the key. When I plug in the key, lights goes on, radio, moonroof works fine.
When I turn it to ignition and keep it there, it makes a few cranks, but very slowly: something like "crank"....silent for a second, then another "crank" and silent for two seconds, another "crank" and dies, no more cranks. When I unplug the key and try it again, it does not make any more cranking noise. It feels like it's trying to start, yet somehow it does not have enough power to turn a full cycle. But that few cranks used up all the electricity in the battery leaving no electricity for me to do another try. That's my impression, but I may very well be very wrong. The battery guage on the dash board indicator stays between H and L, yet very close to L.

I browsed the online information for the starting issue, one of the suggested possible problem is that the engine computer do not see the cranksharft position. If so, the check engine light will not light up when I try to ignite it. So I tried it on my Ford while I have my jump start cable connected to a running car, and found check engine light never come on when I turn the key to ignite. Does that mean my cranksharft position sensor is bad, or it might be at least part of my problem?

I was looking at the battery gauge and found the following: when I use a external battery/jump starter, the indicator stays very close to "L" end; while when I am using a jumpstart cable connected to the other running car, it goes higher, closer to the middle. Does that mean my battery is possibly OK? I know I really should use the multimeter to test it, but before I get access to it, I am trying to give it a little guess. Please correct me if wrong.

Then I noticed the engine oil pressure gauge. My memory is a little vague on this part when I am writing this up, I am pretty sure, but not positive about what I am saying in this paragraph. While I have my key on "ON" position, the indicator sits below "L". While I was trying to ignite the car, the oil pressure indicator goes to the middle. At the mean time, the indicator on battery voltage gauge goes slowly down until it's below "L". The engine makes a few very slow "cranking noise" (if I understand the "crank" word correctly, but that's the noise trying to start). But sometimes the oil pressure light does not go up immediately when I turn the key to ignition, instead, it stays below "L" first for a little while and then jump to the middle. When I let the key go back to "ON" from "ignite", the oil pressure indicator goes back to below "L".

Also I want to mention, the "very slow cranking noise" I was talking about seems to be "less slow" when I am using my jump start cable than I was using the jump starter. And it does not kindof dies off after a few trials. My guess is that my jump starter battery got depleted after a few trials while my jump starter cable has no such problem.

Since I heard about it, I decided to press on the accelarating pedal on my running car while I was trying to start my ford, so to give it a little so-called-"juice". But this time, very similar to what I saw when I connect the well-charged jump starter to the battery, without even putting the key in, something under the hood starts to make a lot of noises, some of them are very quick clicking noise, some are the belt trying to turn (I saw the belt trying to turn, is that the "starter"?). Meanwhile, the Theft indicator on the panel flashes very quickly, and some other lights on and off as well. That's even before I put my key in.
I apologize that I might have described it in a messy way and may give you headache. It is major because that I have little knowledge about cars yet want to make sure I describe everything I saw. Please help. Thanks so much!