Why is my touchpad not working - locks my Surface Pro 3

Hi there,

Every time I touch my touchpad (which usually acts as a mouse) on my Surface Pro 3, my screen turns off. It doesn't shut down the whole tablet, it basically just locks it. The mouse icon might move slightly with my finger, but after about a second my screen goes black. I can touch a key on the keyboard to turn the screen back on, and log back in, but if I use my touchpad again the same error happens. So my keys work fine, but my touchpad does not.

I tried to toubleshoot this and held the Power and Up volume buttons for 10 seconds, when I saw a factory re-set type of screen the touchpad worked fine, so I know that it does still work.

Can anyone help me with this? I know I can just touch the screen instead of the pad, but I'm so used to using the touchpad, I'd love to be able to use it again!

Thanks!