UPDATE 2/10/16:
Now it seems to have died completely. It won't charge when I plug it into a wall or be recognized when I plug it into a computer. Any ideas? Anybody??

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original:
So there's plenty of info out there about the boot loop with this phone, but I can't find anything about exactly what I'm experiencing. If I press the power button, sometimes it doesn't do a thing. Other times, the start screen appears ("htc - quietly brilliant" - the irony), but abruptly disappears. And, sometimes, the start screen appears and abruptly disappears without me doing anything. This has been a progressive situation in that when I first started experiencing it, I got the phone to boot fully a few times, and then after a while it would crash. Now I'm not getting past that start screen at all.

Also, when I try to access the recovery mode screen (volume down + power button) sometimes the screen comes up, sometimes it doesn't. But even when it does, it disappears within a couple of seconds, so I don't have any time to do anything. When I can see the recovery mode screen, it says "***TAMPERED*** near the top of the screen, so not sure if that has to do with anything.

Any ideas? It's not bricked as it still tries to start.

 

Well, I ended up fixing it myself. 79 views and not one response. Some forum...