FIRST, I want to thank EVERYONE on this thread for their suggestions, because I finally got my phone working because of what you wrote. My phone started boot looping today and I had a w2 form from a former employer that was saved in my SMS. I had lost it once and had to get him to send me a digital copy and I was deathly afraid to ask him again for it. I pretty much spent the entire afternoon watching it boot load until i read this thread.
So. Some things from this that I'd like to share, in hopes that it might help some of you out there.
1. I might be wrong, but it seems there are different kinds of boot looping, one from a problem in the OS and one that is more physical/circuitry related. I've experienced the OS bootloop one before on a previous phone, but I knew this boot looping was really strange because the point of the load screen at which it would decide to shut down and loop at was different each time. After reading this thread, it being a problem with the power button made a lot of sense to me, so i started trying to figure out different ways to manipulate the start button when I booted the phone. (keeping it pressed down, pressed down with the other buttons. just a lot of gimmicky stuff).
What ended up working CONSISTENTLY for me was opening up the battery, and PRESSING/sliding THE BATTERY DOWN into the connection to make it stronger. Turns out, what was happening was that that there was a problem with the connection. When I was finally loaded into the OS, it would be fine for a while if i didn't hold the battery down, but the power menu would keep popping up like I was constantly pressing the power button down a little bit, and then releasing it. after 4-5 minutes of not pressing the battery down, it boot looped again. Keeping a tiny piece of plastic wedging the battery down has fixed everything so far.
2. I don't really understand why it was still booting on even for a little bit if there was connection problem, or why this weak connection tricked the phone into thinking the power button was being pressed, but my guess is that the weak connection causes a short or some sort of current change (my memory of the circuitry section of my physics class is really weak; probably something to do with electric switches??) and this current change mimics the circuitry of what happens when you press the power button down, therefore causing a more "physical" boot loop.
I don't think that this is the case with most boot loops, most being a problem with your cache or something more systems oriented, but if your boot loop symptoms are like mine and the original poster's, perhaps this information helps.
UPDATE:
If what I surmised was even close to reality, then this circuitry problem seems to be degenerative. I was able to get on for about 30 minutes and retrieve a bunch of files that I needed and email them to myself. After that it began boot loading again, and now it seems that nothing will keep it on.
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