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When you ran the RUU, you un-rooted your phone. When it failed in the RUU, it bricked your phone. I am using the term bricked fairly liberally, btw. What you are going to need to do is
- get the phone into the fast boot
- power off (doesn't seem like it will be a problem
)
- power on while holding volume down
- do NOT hit anything else
- plug in the phone
- run the ruu while the phone is plugged in on that screen
- if all goes as planned, it will complete and power cycle
- re-root the phone, do a nandroid back up
- enjoy
The RUU completely unroots the phone. After you first root it, that nandroid backup you make will be your return to stock. Always keep that one. if you are going to a sprint store, they will have almost no way of knowing you rooted the phone, and only very few associates there will know how to check, and even fewer of those will even be motivated to check. The RUU is only for situations like the one the RUU put you in in this instance. Let me know how it goes.