can't type more than a few words without ---

So I'm typing a response to a Youtube video and part way through my comp. changes screens to something else.
Then I have to find it (the place were I would have responded) again and it happens again. This happened with windows 8 and I just let my comp. update to 8.1 and it still happens. Any ideas why this happens?
Been around a while but this baffles me.