Allow Excel 2010 to open separate windows.

There is no real trick to getting Excel 2010 to open two screens side by side.  There’s many tricks out there but none seem to work properly, if at all.  Registry hacks can work but then other problems can arise and you need to fix those issues.  Then you get in deep over your head and need to call a technician.  Embarrassed to say what you did, the technician maybe racking up the hours trying to fix the registry because you probably didn’t back it up first.
It’s simple, have a shortcut to Excel on your desktop.  Not a shortcut to the individual files, but a shortcut to the main Excel 2010 program.  Open Excel, click File and open your file.  Next, minimize that Excel document or move it to your other screen, out of the way so you can see the shortcut to Excel 2010.  Open the second instance of Excel 2010 via the shortcut on your desktop.  The second window comes up blank and available for you to go to File and open your second spreadsheet file.
Now you have two windows/instances of Excel 2010 at the same time which you can either overlap, side by side on same screen, or if you have two monitors, you can have one on each monitor.