If you can’t open the Start menu after update KB4517389, use these steps to roll back to a previous build and fix the issue on Windows 10.
As part of the October 2019 Patch Tuesday update, Microsoft rolled out update KB4517389 for devices running the Windows 10 May 2019 Update (version 1903) to address several problems, including for printing, performance, and security. However, shortly after the release, a small number of users began to report that after applying the update, the Start menu stopped working.
According to some users on Reddit (via Windows Latest) and Microsoft forums, immediately after installing the KB4517389 cumulative update — which bumps the version to build 18362.418 — the Start menu breaks with “Critical Error, Your Start menu isn’t working. We’ll try to fix it the next time you sign in” message.
If the problem sounds familiar, that’s because during the September 2019 Patch Tuesday rollout, Windows 10 experienced a similar issue, and even though it was later labeled as resolved, it appears that this isn’t the case.
Via:: Windows Central