If you encounter this issue, you can reset this in registry as follows:
In the registry editor, search for HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Notification\Settings\Microsoft.Explorer.Notification….
There may be multiple items. Click each until you find one that states has a REG_DWORD with a value = 0.
Change all their values = 1.
Reboot your machine (may not be necessary) and try again.