If you open two sessions of Excel (clicking on the Excel icon twice), this
will disallow referencing the other sheet.

Better to have one open in an instance, then open another using the File -
Open menu.

Once both are open go to Tools - Options - View tab - Windows in Taskbar.

Now you should see two windows and be able to reference across workbooks.

"Osama" wrote:

I have figured out how to open two excel files in separate windows. However,
I realized that many functions had been disabled by this option. I have tried
to reverse the process to go back to the original (defulat setting) but no
success! Any help in this matter?