To start off, I have owned a Droid 1 and Droid 3 and have modded, rooted and all of that jazz. I attempted to root my girlfriends Droid 4 while on vacation in Texas using the Droid 4 Utility for Windows.
It would initially work, then have some weird "power" issues. The screen was "dead" where it would be at the lowest brightness or not on at all. Can't verify. You could still technically use the phone and feel the vibrations on the screen but no display. A reboot would temporarily give you a display but as soon as the phone went to sleep it would repeat.
Since then there was a firmware update that seemed to rectify a power issue with the phone. I figured I would give rooting it one more try. Downloading the utility again it seemed to work. Girlfriend hits me up today and says it happened again. I unrooted the phone and in theory as of now it is working again.
My question, why would rooting cause this issue?