To open multiple sessions of excel from file explorer (open files in new windows), do this on the server under your admin account (this will apply the change to all users.)
Open MY COMPUTER
Select TOOLS/FOLDER OPTIONS
Select FILE TYPE tab
Select XLS, ADVANCED button
Select OPEN from the list
Select EDIT button
Place cursor at the end of the path by "APPLICATION USED TO PERFORM ACTION"
Add to end of path- (space after /e) "%1"
Example: "C:\Program Files\Microsoft Office\OFFICE11\EXCEL.EXE" /e "%1"
Uncheck "use DDE" box
Click OK twice
Click CLOSE