Open Excel files in new window

"I've had this problem too. Here's what I did:

In Excel 2003, go to Tools -> Options
-> General tab.

Make sure the option, ‘Ignore other
applications’ is checked.

In Excel 2007 & 2010, Click the Office button
-> Excel Options -> Advanced.

Under General, check ‘Ignore other
applications that use Dynamic Data
Exchange’.

I don't know why this isn't built in.
Source: http://www.lytebyte.com/2008/05/13/how-to-open-two-excel-files-side-by-side-in-separate-monitors/"

"There are certain disadvantages to having all your workbooks opened in different windows. For one thing, if you write a formula in one workbook which references another, it will include the full file path of the other workbook. For another, copy/pasting from one workbook to another reduces the number of options available for the destination data, like keeping the column widths, etcetera. It's possible that for your purposes those things won't matter much, but basically if you experience any ""weird"" behavior when using multiple workbooks in multiple windows, you might try opening them in the same window to see if the weirdness goes away.

My preference is to leave the default behavior to open Excel workbooks in the same window, and when I want individual workbooks opened in different windows I right-click the file and select ""Open in new window"". In order to do that, I wrote this small utility. It's free. Feel free to install it."

Since hyperslug's answer didn't work for me, I followed "Option B" from his link and now open a new (empty) Excel from the start menu and drag'n'drop the file I want to open into the new window.

In Office 2013 they solved this issue. Each workbook is in its own window in Office 2013.

"Here's another set of registry files I (which I created) to solve the same problem: http://www.experts-exchange.com/Software/Office_Productivity/Office_Suites/MS_Office/Excel/A_1007-Option-to-open-excel-2007-documents-in-a-new-instance.html?sfQueryTermInfo=1+30+excel+instanc+new

Gives a right click menu to open excel files in a new instance, and optionally makes it the default behavior, but still leaves the option to open it in an existing instance if the workbooks need cutting and pasting with formatting between them."