What exactly do you mean "failed to open"?
Doesn't the program run at all, does it fail to conect to the server, does it connect to the server but not show the inbox on the screen, or did it fail to read new mail from the opened server into the inbox shown.
Any error message?
Does System Restore back to before yesterday solve the issue?
Just yesterday, my WLM decided NOT to open. Don't know what happened, but super annoying.
I upgraded to Windows 10 about 6 months ago, and it was working fine. I'm using a PC that is about 7 years old, but kept clean and updated regularly.

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