Red M pops up and disappears as normal, then it just sits at a black screen forever. I kept it on the charger and then unscrewed the battery terminals to keep it from going flat.
Hopefully that's enough to support charging. Right now all you can do is apply updates and perform factory resets. I don't know what to tell you, wipe cache, data, everything. There's not much you can do at this point.
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It's weird that Doc is getting bootloops. My only suggestion is to keep applying the update, maybe one of his attempts will stick.
I know people want to avoid sbf so they can save their data, but I prefer SBFing so there are absolutely no problems. I was able to sbf, flash the update, and root in about 45 minutes. I remember similar problems going from GB to ICS and people always ended up SBFing after going through all the trouble of finding the problem.
After two tries with Razr Blade, I got properly rooted!