Hi Ali Tarkesh,
I know how disruptive it can be when you're trying to use Office and an error like this appears. That message typically relates to User Account Control (UAC) or system security settings in Windows. Let’s go through a few steps that may help resolve it.
First, try running the Office app as an administrator. Right-click the shortcut, go to Properties, then the Compatibility tab, and check Run this program as an administrator. Click Apply and OK.
Second, if you're using Windows Pro or Enterprise, open the Local Group Policy Editor by typing gpedit.msc in the Run dialog. Navigate to:
Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options,
and disable the setting called "User Account Control: Only elevate executables that are signed and validated."
Third, Be cautious and back up your registry before making changes. If you're comfortable using the Registry Editor, press Win + R, type regedit, and go to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System.
Set both ValidateAdminCodeSignatures and EnableUIADesktopToggle to 0, then restart your PC.
Fourth, you can temporarily lower your UAC settings. Search for UAC in the Start menu, move the slider to Never notify, and try launching Office again. Just remember to restore the setting afterward for security.
To better assist you, could you share the exact error message you're seeing? A screenshot would be very helpful if you're able to upload one.
Let me know how it goes I'm here to help!
If this resolves your issue, please mark the answer as accepted so others can find it easily.
Best,
Carl