It's not that - I found a thread about that on Steam yesterday but I haven't got any Razer stuff, double checked anyway and definitely none of their software either. The only things that have changed recently is a Steam update, an nVidia driver update and a Windows 10 update. Tried rolling back the nVidia driver but it made no difference. The Windows update is for the new version of Edge and isn't easily removable, and Steam doesn't let you roll back. Tried going onto the beta channel in Steam but that didn't help either.
Thanks for trying to help, much appreciated
I'll keep fighting with it!