Excel opens files in separate program instances that can't move tabs or paste special

I use excel 2010 on 2 computers at home, and 16 computers at work. All 16 computers at work and 1 of the computers at home open excel files when they are double clicked in the same instance of the program if a excel file is already open. However, the computer I use the most at home opens double-clicked excel files in separate instances of the program every time, and then functions like Move or Copy sheets to other open workbooks, or paste-special functions from one workbook to the other (like formats, column widths, values, etc) are no longer available between the two or more open files. However, if I open a 2nd file by clicking through the file, open menu or pressing control+o from the first opened file, the file opens in the same instance of the program and all previously mentioned functionality continues to exist as expected.

This is very frustrating, and all the searching I have done reveals tons of results from people who actually desire to cause the program to act this way (at least in terms of opening in separate windows) for whatever reason. I do not want the program to open files in separate instances or windows, I just want my functionality back. Does anybody have any suggestions or knowledge of some setting or registry hack or something that I can do to fix this?

Any help is much appreciated.

I posted something similar a long time ago and never received a response, but I think this is a better explanation of the problem. If anyone wants to see the old post, it is here: http://www.excelforum.com/excel-gene...mmunicate.html

Also, here's a post of lots of people being frustrated with the same problem in other windows programs on answers.microsoft. Lots of people complaining, no solutions offered... http://answers.microsoft.com/en-us/w...cfefb29?page=2
I don't have this problem with anything outside of Office 2010 though.

have you seen this answer:
http://superuser.com/questions/47963...cel-2003-in-wi

Thanks for the reply. Yes, I've seen and tried all of these fixes and/or workarounds with no success. Any other ideas? I did see someone somewhere talking about a manual change to the registry, which may be my only option at this point, but they were referring to an installation of office 2003, not 2010... I didn't try it at the time because I'm very unfamiliar with registry hacks, and have a different version.