Standard Acer Extensa 5220 laptop running Vista Home basic and AVG antivirus.
The Windows Update service hangs when it is started by svchost. It displays in Windows Task Manager as "starting" but when you select "Stop Service" from the right-click menu the message displayed is "The operation could not be completed. The requested control is not valid for this service." The calling Svchost.exe process hogs all the CPU so that CPU Usage goes up to 100% and stays there indefinitley, with fairly predictable results on the performance of the machine.
The only way I can find to make the machine usable is to put the service on manual start. If I subsequently start Windows Update from the Start menu, it hangs, the CPU goes up to 100% but the service still displays in Task Manager as "stopped". Occasionally the Windows Update window allows me to "check for updates" - but it just reports "Windows cannot currently check for updates, because the service is not running...". This, of course, means no more updates. Usually the Windows Update window will not close.
I see that problems with Windows Update go right back to 2007. Despite similar problems haunting hundreds if not thousands of users I have not been unable to find a fix. Is there one?