This fix is using Vista and IE explorer. Make sure you have a file saved on your computer that you want to open with Excel. I would suggest deleting Microsoft Office off your computer, then restarting your computer and reloading Microsoft Office and all the updates. Yes I kinow its time consuming but the end results are well worth being able to open an Excel .xlsx file with no hassle.
Next click start and go to your Control Panel. Make sure it is in the Classic View. Scroll down the page to the Folders Options Tab (or Icon). Open it up. Go to the View Tab under Hidden Files and Folders select the radio button for Show Hidden Files and Folders. Select OK and close. You can go back after the FIX and change this back.
Next: I alread had saved a .xlsx file on the desktop that I couldn't open with Excel in its present condition. Right click on the File and go to the bottom of the page to the word Properties. Left click on that. The List Properties will open up. Go down to the "Opens With ....... and select the Change Tab. Go down on this page to the Browse Tab (right hand side) and select that.
At the bottom of this page above the Open - Cancel Tab is a drop down window select this and choose All Files. Scroll down the folders tab to Microsoft Office (left hand side) and double click on it. Scroll down to a folder called Office 12 and double click on this. Scroll down on the right hand side of your page to the EXCEL icon. This will be located under a folder called "Envelope.DLL" and above a folder called "Excel.exe.manifest". Select the Excel Icon and hit the open tab. Close everything and your file will open right up!