Microsoft Excel, how to open 2 excel windows

Start > run > regedit:
Left column
HKEY_CLASSES_ROOT/Excel.Sheet.8/shell/Open/command:
Double Click on (Default) and add space "%1" For example: "C:\Program Files\Microsoft Office\Office14\EXCEL.EXE" /e "%1"
Right Click on Command – choose "rename" and add something to the name. For example: command2.
Left column
HKEY_CLASSES_ROOT/Excel.Sheet.8/shell/Open/ddeexec:
Right Click on the folder ddeexec and choose "rename" and add something to the name. For example: ddeexec2.

Left column
HKEY_CLASSES_ROOT/Excel.Sheet.12/shell/Open/commend:
Double Click on (Default) and add space "%1" For example: "C:\Program Files\Microsoft Office\Office14\EXCEL.EXE" /e "%1"
Right Click on Command – choose "rename" and add something to the name. For example command2.

Done, no restart needed

For microsoft official  addon to open 2 excel window: Download