Auto update not working anymore

Hi,

since some weeks ago I noticed, that auto update doesn't work anymore
properly. It doesn't finish to download the updates. I also cannot download
them via Microsoft update (or Windows update) - it stops after I accept the
EULA for WGA. If I deactivate the service "autmatic updates", Microsoft
update refuses to work at all.
The interesting thing is, I even cannot configure automatic updates anymore
in the panel of "system". It seems to be corrupt and this although nobody
changed anything at the computer and everyone works as limited user. What can
I do to repair automatic aupdates? Please don't say "reinstall". It took a
lot of work to configure the computer like that.

Best,
Mat