Last udates;
Sat Aug 15 Update KB961118 (did not have second monitor hooked up)
Fri Aug 14 Update KB951847 (Last day second monitor working...updated at
shutdown)
Have you tried uninstalling both updates and rebooting?
NB: Do NOT attempt to use System Restore unless and until you've uninstalled
both updates! If you've already done so, you're really up the proverbial
creek now.
Are there graphics driver and/or monitor driver updates available (from the
respective manufacturers' websites)?
Have you tried (1) disconnecting the secondary monitor, (2) rebooting, and
then (3) reconnecting it?
Truth be told, I'm sure KB961118 didn't cause the problem. If installing
KB951847 caused it, I presume it's only because the hardware is outdated or
you need driver updates (assuming you're running WinXP SP3).
PS: I can show you a way to remove .NET Framework 3.5 Service Pack 1.
Whether doing so would correct the problem, I dunno.