For some strange reason windows update no longer works. For the last few years i have had it set so it tells me when there is an update available but lets me decide when to install it. But now when i download the update it no longer installs. It tells me it is installing but next time i switch on my computer its not installed.

I already have AVG installed and Zone alarm as well as A square and they find nothing.

So my question is windows update broken or is there something nasty buried in windows on my computer that is blocking the updates?