dual mon not working

Here's an interesting scenario.

I've got this issue on two XP SP3s. We got dual monitor AGP cards in both.

Two LCD monitors have been working on both machine just fine until one

Microsoft update later and one monitor is not working anymore on each

computer. I have swapped monitors and cables with known good ones, and that

is not an issue. The Display applet in Windows shows both monitors but when

you click on number 2 and put a check in the box to extend your display and

click Apply, the screens go blank for a second and come back with only the

first display with the box unchecked.

These two machines are in different buildings. Uninstalling and reinstalling

display drivers don't fix the issue. Downloading the entire ATI suite (one

of them is a Fire GL V5000) and loading that doesn't fix it either. In fact

the ATI application shows only one display available on the machine that I

tested this on.

On the other machine I restored the system back a month and both displays

came back. This does not fix it with the machine with above mentioned ATI

card.

Please help.

Thanks,

FM