OK, how did you root it, and what did you do to unroot it? These might give us information about the state of the device.
How are you trying to reset it? My guess is that you are using the system Settings, so have you tried going into recovery and resetting from there? What happens if you do? (That last might tell us why resetting from Settings doesn't work).
Finally, why are you trying to reset it? A reset will not undo any changes you have made to the system software, all it does is wipe your data, so if the reset is related to what you are trying to do in unrooting it's not likely to help.