Yeah if you have USB debugging on and try to install the drivers it won't work. The first time you install drivers you need that off then you can go back into it. Normally it woudn't matter cause you could change to pc media sync cause those are different drivers. But since you can't even boot up that is your problem.
Best I can tell is Windows sees your phone differently when you have debugging on. Cause I turned it off and uninstalled drivers then plugged it back in and reinstalled and it worked. Then I was able to turn debugging on and RSD saw it just fine. I was telling you about the Media Sync mode because RSD saw my phone even without the drivers. Can you take it to a Verizon store and have them flash back for you?
Well they already have the drivers installed and working I would be willing to bet their computers would pick up your X. Unless you close to the Austin Tx area I can't be much help.