Shouldn't need new key. Licence server should recognise it as the same PC and let it use the existing key. Uninstalling does not remove the key from the PC.
Is it OK when you print it ? (i.e. is it just a display issue), does print preview work?. Maybe check for updated graphics driver, or roll back to an earlier one. Try toggling 'advanced 2D rendering'.
Have you re-booted the PC - occasionally things get 'stuck' and require a reboot to resolve.
That suggests that either your graphics adapter, or its driver, doesn't support the shader functionality that is required for advanced 2D rendering (or something else is interfering with that).
I've just looked back at some earlier threads about the same issue. It may be worth you turning off anti-aliasing in the control panel for the graphics adapter, advanced 2D rendering may then work.