Do you use Steam perchance? Theirs and Windows recent update did not get along, which apparently caused more than a few issues. If so, you can remedy it by deleting every file in your Steam folder except: Steam, Steamapps and userdata. The bin may or may not delete, but restarting and reinstalling Steam afterwards will fix it regardless.

If not, then you may have to reinstall FFXIV as it sounds like there's a conflict between it and Windows 10.