Well, this really has nothing to do with VBA and it's not asked in the right place, but there really isn't a right place for this as it's either video driver related or a simple fix. Let's go simple first.
Is the code window not maximized but rather restored? In other words, can you click the maximize button and have it entirely fill both monitors, or is only the restore button next to the close button on the code window? If the maximize button is there, resize your form to the monitor you want it to, from which point the maximize should work to fill that one monitor only.
If, however, clicking maximize fills both monitors, then that's a video driver issue. I've got NVIDIA cards on my computers with dual monitors, but both ATI and NIVIDIA do the same thing -- just the terminology is different. Basically, you'd have to go your video card's drivers and in the multiple monitor control panel (called Dualview in NVIDIA drivers), you have to set one monitor as your primary monitor (the one that gets the Start button, the taskbar, etc.) and set the other to be independent (hence, "dualview").
It sounds like they somehow got changed to be one long horizontal monitor. You can tell this quickly if the taskbar goes across the bottom of both monitors, as in the clock is in the bottom right of one monitor and the Start button is in the bottom left of the other.
