I am having the same problem with my Surface Pro 3, although I can still get the on screen keyboard to come up. I have not upgraded to to win 10 pro, just the standard win 10 upgrade from win 8.1.
And no, none of the fixes posted have worked for me either.
Yes the problem started after an "automatic" upgrade.
Guess what, the last upgrade to my lap top also killed some functions on it that have been working for over 2 years. For some reason, it seems that my previous restore points created when both devices worked, have disappeared.
I cannot afford to purchase new equipment every time microsoft upgrades cause my equipment to lose previously working functions. These upgrades may be designed, in someone's mind, to improve my computer's functionality, but they seem to be playing havoc with way too many people for the failures to be just a coincidence.
At any rate, thanks for trying to help us all.