Won't install dowloaded Windows updates?

For the past couple of months, when I shut down my laptop I get the usual options. I nearly always opt to shut down and install updates. The system tells me that Windows is shutting down, do not switch off computer, installing updates... I always let my laptop go through the motions and appears to install the aforesaid updates. Next day when I switch on in the system tray I get a message saying updates are ready to install... And the same routine has been going on... Laptop appears not to be installing or ignoring the updates Anyone help?? Please!! Fujitsu Amilo Pro V8010 running XP with Avast, Comodo firewall, Spyware Terminator and Spyware Blaster