I bought a pc with Windows 7 that has worked fine with Word (office 2007). However, when I save a file with Excel 2007 and then call it up, the ribbon no longer works (I click on the various commands and ribbons don't pop up). Likewise, I cannot make cell entries or try operations like sorting. However, the program has not frozen since I can click on the various worksheets on the bottom. Is this an Excel or Windows problem and what is the solution.