I use the following script batch file to force Windows Updates or the WSUS client to start the update process:
@echo off
rem Stop the Windows update service:
net stop wuauserv
rem Delete registry keys that store information about the last update.
REG DELETE "HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update" /v LastWaitTimeout /f
REG DELETE "HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update" /v DetectionStartTime /f
REG DELETE "HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update" /v NextDetectionTime /f
rem Start the Windows update service:
net start wuauserv
rem Force detection of updates
wuauclt /detectnow
rem Sleep 4 seconds so you can read messages:
ping localhost >nul