|Windows XP (and 2000) often enables only one display by default. |
(This info is probably in the Help info in Windows, and/or in the Help info for your display adapter)
Go to Control Panel - Display Properties - Settings.
Hold your cursor over the displays - if one is disabled you will see "Not Active".
In that case, RIGHT click on the disabled display and enable it. You may need to reboot as well.
If that doesn't help.....
ATX mboards are always powered in some places by the ATX PS, even when the computer is not running, as long as the PS is connected to the mboard, the switch on the PS is on if it has a switch, and the PS is connected to live AC.
If you make any changes to connections, including to drives or to the PS, or install or remove any components inside the case, if you haven't removed the live AC power to the computer when you do that, you can easily damage something.
If that doesn't apply....
If the monitor ports you are connecting to are both the ports on a video card that's installed in a slot, NOT ports near where most of the ports are located in the I/O area, the video probably supports using a DVI to VGA adapter.
If the ports you're connecting to are for onboard video and ARE ports near where most of the ports are located in the I/O area....
I noticed when I was looking at new mboards early this year that some recent mboard's main chipsets onboard video will not allow a standard DVI to VGA adapter to work because the wiring isn't there. In that case, if you look in the User manual or similar for your brand name model, it will probably either not mention using a DVI to VGA adapter, or it will tell you the mboard does not support using one.