Whenever I try to launch Shadow of Mordor I can see it running in the task manager but no window ever appears for it. This happens with a gog galaxy install and with the offline installer on Windows. Has anyone else encountered this issue? Thank you!

I don't own this particular title, but I am having the identical problem in many of the other titles I have in my GoG Galaxy Library. I tried using the self installer on a game and had no issue running it again. Only thing I can think of now is to reinstall Galaxy again, other than that not use Galaxy at all and just go from the Website. Whether it's something that's altered following a Windows update that Galaxy doesn't like really don't know. Galaxy itself says it doesn't require an update, but have noticed the text can seem blurry randomly, but focuses when I move the side scroll bar.
Good Luck, If you find a solution, please update your post and let us know. Cheers

Simmilar Issue here.I used to be able to run the Game and played thou most of it. After a few months break, I decided to play the last DLC, but the Game only ever launches into a blackscreen.

I tried Running it in Compatibility mode and/or as Admin, but that did not help.

Did you fix the problem? I have the same issue

It would be best to contact support. Maybe they can help you