If you run Windows or MS update it won't automatically list .NET v4 as it is not considered a "High Priority Update". Instead, you need to look in the panel on the left side of the screen and choose "Software, Optional".

I'd suggest trying that first as it's likely there other updates listed there that could make a difference, such as those for Microsoft Visual C++ redistributables. FWIW I just checked and found two stability updates for .NET v4 there.

Regards,
Frank