What CMS / player versions are you currently using please?
you can try to use IE 11 and make this registry change Enabling HTML5 in the Windows .net Player
Or just install IE 11 and Xibo for Windows 1.7.8 (it will make this registry change during installation)
Not sure what could’ve changed since it was working for you before.
Are there any errors in CMS logs (with debugging enabled of course) and/or on a player status window?