Approximately a week ago I started to experience a lot of bizarre problems -
namely settings changes, updates unable to be accessed and installed,
intermittent update icon in tray that wouldn't permit download of updates,
update icon at turnoff that also wouldn't install updates.
Try this fix.
http://support.microsoft.com/default.aspx/kb/927891
At least for me, it appears to have fixed the above mentioned problems.
Although, when you install KB927891 it doesn't show up on your update
history, nor does KB916089 - which 927891 is intended to fix.
All these bizarre problems with updates and consequences for PCs is nothing
new. MS had serious problems back in 2005 and never offered any definitive
fixes.