.
I'm using Excel 2007. As far as I know, all versions of Excel use a "startup folder" from which Excel knows which file to open when it is started.
My system uses this path to get to the XLSTART folder : C:\Users\My\AppData\Roaming\Microsoft\Excel\XLSTART
Look in your XLSTART folder and see what workbooks are residing there.
There is also a setting in the Registry that can be edited to specify which file to open when Excel starts. You'll need to do
an internet search for instructions.