I'm running Excel 2003 on my new Windows 7 machine. (There is also a Excel 2010 starter pre installed that I do not use).

I'm a heavy user of Excel. I use it all day every day. I often have 10 or 15 sheets open and once and many of them have cell references to each other. I also have a macro file that keeps all my short cuts.

On my old W2K machine when I clicked on a .xls file or a shortcut to one to it would open that file in the existing instance of Excel. This is as it should be. I would have many files open, in only one "window" or instance of Excel. All the files could interact with each other, the cross file lookups worked, my macros worked and I could switch between workbooks with CTRL Tab or CTRL F6, I could move tabs from one workbook to another.

On the new W7 machine clicking on an icon opens a NEW INSTANCE of Excel every time. This is terribly frustrating. None of my connecting spreadsheets work anymore. My macros don't work. I can't connect files, I can't move tabs. I'm stuck. I can't do my work!

I can still open files in one instance by doing a CTRL-O and navigating, but I need to my files to work on a click.

I'm guessing this is a flaw in the registry files, possibly because of the starter Excel 2010 that came preloaded on my new machine.

Can you walk me through a registry edit to fix this bug? Is there an easier way than a registry edit?