You may see the following error message when manually checking for Windows Updates on Windows 7:

This is usually intended behavior, caused by a policy from an administrator. To remove this policy and check for updates and install them, change the following registry entry from 1 to 0:

HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\NoWindowsUpdate

HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\NoWindowsUpdate

HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\WindowsUpdate\DisableWindowsUpdateAccess

You should be able to check for updates now. No restart required!