Problem: After weeks/months/years of trouble-free operation, various programs such as Word, Excel, Acrobat etc. start popping up their dialog boxes on the "wrong" monitor in a multi-monitor display.
For example, the "Find" or "Format cells" dialog of Excel may appear on the right-hand monitor instead of the center one, or on the center one instead of the left-hand one. Or, for dual-monitor displays, it shows on the left if Excel is on the right, or vice-versa.
Possible solution: If you are running an AMD FirePro graphics card, chances are your monitor settings recently got f^ck@d up for no apparent reason at all and completely scrambled your nice monitor setup. God only knows why this happens at all (I sure don't) but I'll bet it happened to you.
You went through all the pain of resetting monitor positions in the Windows Display settings, because your left monitor became your right, your center became the left, etc. And (probably) re-organizing all of your 100s of desktop icons on your displays which similarly got scrambled, and your damn icon restore programs didn't work. Now you find that dialog boxes are effed up as well.
If all of the above is true, the culprit could very well be the AMD Catalyst Pro Control Center setting called "Enable Dialog Repositioning". It is buried in Catalyst Pro Control Center under Hydravision / Desktop Manager. Chances are it is enabled and set to "Show on preferred display" where the "preferred" display is NOT the one you want.
To fix it, you can turn off dialog repositioning completely - I really don't know why it is there in the first place - or you can reset it to "Show on application's display". You may need to try both settings to see which one works better.
Of course, if you prefer dialogs to appear on one of your displays all of the time, you can keep it set to "Show on preferred display". Just make sure the number of the "preferred" display, waaay off there to the right, is actually set to the one you want to call the preferred display! It does NOT automatically default to the Windows "main" display.