first and foremost - why is it vibrating so much?
I'd start by looking into that, as it may be an indicator that something more serious is going on with the mill other than just the LCD display (side effect).
as for the LCD - seeing that it operates normally in most cases, I would think the display and reader are just fine, and the culprit is more then likely with the cable connections - you can take apart the LCD display by unscrewing the 4 allen bolts that hold it to the mill head and it pops right out (forward) - check the connection and make sure they are seated properly all the way in - also take a look at the PC cable itself and see if any damage to it is visible. Next - take apart the back panel of the mill column (the smaller rectangle panel in the back) - this will give you access to the other end of this cable - make sure it is connected properly and undamaged on that side as well.
if you are unsure, you could post pictures of these areas and we might be able to help a bit more that way.