I've been trying to set up a laptop for someone and ran into this issue.Some Windows 8.1 users who have installed the September 2017 update KB4038792 report that the installation broke Microsoft Account sign-ins on their devices.
[...] They receive the following error message when they try to sign in to a Microsoft Account on affected devices:
Sign in to your Microsoft account
Sorry, we couldn’t connect to Microsoft services right now. If this problem persist, search for “network problem” on the Start screen.
A Microsoft support employee confirmed the issue on September 22th, 2017 on Microsoft's Answers forum. A customer reported the issue on September 16th, 2017...
Microsoft promised that it will update the thread on the Microsoft Answers website when the update is available. [...] It is unclear how widespread the issue is. Microsoft said that it affects a small subset of users only.
Source 1 and 2.