Are you sure thats an Excel file? Its telling you that it can't find data in the fist few rows. Open it in Excel and see what it looks like.
For the icons, that a different thing. File associations are given by the file extension. By default on install, .xlsx, .xls etc. will be associated with the Excel application, you can of course change this, and maybe this is what you have done. In windows, you can right click on an .xlsx or .xls file and click Open With. Now select Excel from either th list presented, or the other items, and make sure Always open with this app check box is checked in lower left. Now click ok, and the Excel icon should appear on all these again.
