ZDNet noticed many users are complaining online about a Windows 7 issue that prevents a system shutdown. Oddly enough, the bug only appeared in the last couple of days:
A "You don’t have permission to shut down this computer." error is preventing Windows 7 from shutting down or restarting their computers according to user reports that came in during the last 24 hours.Countless reports from Windows 7 users suffering from this issue have hit Reddit, Twitter, and the Microsoft Answers forums.
Until there's a fix from Microsoft (if they even fix it), here's an unofficial fix offered by Reddit users:
However, if you're still using Windows 7, we highly recommend upgrading to Windows 10 as soon as possible.
Step 1: Press Windows+R to open the Run window. Step 2: Type gpedit.msc and press Enter. Step 3: In the Group Policy Editor window go to: Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options. Step 4: In the right panel of the Security Options option,search and double-click on "User Account Control: Run all administrators in Admin Approval Mode." Step 5: In the new window, select Enable. Step 6: Reopen the Run window, but this time type "gpupdate /force" and press Enter. This will update all group policies. Step 7: Restart or shut down your system normally.