Installed Office Professional Plus 2010 on new computer with Windows 8. Can create and open all Office documents except unable to open existing Excel documents. When try to open, I am asked for the activation key. When key is entered, get message that key is not valid. Inserted install disk and re-entered activation key. Did not work. Called Microsoft and they will not help since software is older that 90 days.
Any ideas. Many of our business docs are on these Excel files.