Okay, it sounds like your ATI doesn't know about the other monitor, and since that setting can be OFF though connected, there's a need to turn it ON. I have ATI on my XP machine with two monitors and an HP 6400; my main Win7 also has two monitors, but Intel HD, and yes displayport to VGA adaptor. For the XP, there's a tabbed dialog box for ATI; in Win7, it might be part of Personalize Display Settings, which should reveal if Windows 'knows' you have two monitors connected. Make sure both monitors are ON, and see.
Did you run Windows 7 Media Center? That helped me.
Or, right-click on Win7 desktop, then you should find something worded similar to 'Graphics Options' then a flyout menu gives you 'Output to' and you select 'Extended Desktop': make sure it shows two monitors. But to get the actual settings right, instead of 'Graphics Options' you might see something like 'Graphics Properties', click that and then look for 'Multiple Displays' in the dialogue box. Click on that, and then re-arrange Monitor 1 and 2 as you actually have them placed, plus change the resolution settings (if needed) for each monitor, including RGB etc. as desired. Then click 'OK', and the screens refresh; if you like the setting, 'Accept' it. The foregoing are the menu options for Intel, but they should be similar with ATI; though perhaps you get a tabbed dialog box instead. (ATI is wonderful, btw, but I don't have it on Win7. Hence am guessing.)
These are monitor settings controlled by Win7 and your video card, not affected by the underlying PC.
Edited by brainout, 11 July 2015 - 10:20 PM.