Word and other Office apps appear to hang or freeze, just a blank nonfunctional grey screen is shown when opening files from SharePoint Online (SPO) in the rich client apps.
The registry key:
DWORD value signinoptions
was set to a too restrictive option for your environment.
The value of 0 is the least restrictive and can be used if you are having this problem.
0 – Don't block any sign in UI.
1 – Allow Live ID sign in UI only.
2 – Allow Org ID sign in UI.
3 – Block all sign in UI. only.
4- Allow both Org and Live
Set the "signinoptions" registry value to 0.