An integrated threat protection solution designed to detect, investigate, and respond to cyber threats across Microsoft 365 services.
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Office LTSC Professional Plus 2021 and 2024 are Microsoft Office editions, not Windows OS versions. Please confirm whether you upgraded Office only or also upgraded Windows.
First, disconnect all unnecessary USB devices and restart the computer.
If Automatic Repair appears, select Advanced options > Troubleshoot > Advanced options > Startup Repair.
If Startup Repair does not help, Advanced options > Troubleshoot > Advanced options > Uninstall Updates > Uninstall latest quality update.
You may also try System Restore from the Advanced options screen if a restore point is available.
If Windows Recovery does not appear, interrupt startup twice by holding the power button when the Windows logo appears. Windows should enter the recovery environment on the third startup. You may need the BitLocker recovery key if device encryption is enabled.
https://support.microsoft.com/ja-JP/windows/experience/startup-boot/startup-repair