Default Program

I have Office 2007. I am unable to open or XLS files with microsoft Excel
unless I open Excel and then use the menu to open the file from within Excel.
If I simply click on the file or download and open the file from online the
computer does not respond. I have tried to associate Excel as the default
program for XLS files but it does not work. I have two programs in my Office
12 folder - Excel and excelcnv. There is nothing in my Office 10 folder.
Currently excelcnv is the default set up, but since it does not work i tried
to change it to Excel. I go through the change default program steps but it
does not respond when i open the Excel program. Any suggestions? Thanks