Have you tried rebooting the tablet? If not that would be my first suggestion.
If that doesn't do it, and you can't access the calibration screens at all (to recalibrate the device), the only other option I can think of that you can do on your own is a "Hard Reset", but that I would really save for a last option thing. Why? Well, because it will wipe all your personal data.
If the device is still under warranty, contact the manufacturer and they can repair or replace it. If it isn't, and you don't want to wipe it with the "Hard Reset" (which is not guaranteed to fix the problem btw), then I would contact a local tech or tech shop to see about having them look at it. It may well need the display replaced.
NOTE: Doing this will clear...