Terrain Problems

Hi,

First time poster.

Been working on Unity for a while now, however, recently, every time I create a terrain I cannot adjust its size in inspector.

I have tried using the 'set resolution' which, works fine - however, I cannot modify the height of this terrain.

What puzzles me, is not only have I uninstalled and reinstalled the software a few times, my friend has the same problem on both his laptops :/

thanks in advance for any help :)