Excell Problem while sendig the command

Hi. I have Windows 8.1 Pro and Excell Office 2007 2. These have operated without problem for years but yesterday when I tried to access folders previously saved I get the message 'THERE WAS A PROBLEM WHILE SENDING THE COMMAND TO THE PROGRAM'. I can still save new Excell spread sheets to Folders but when I try to open them I get this fault message. Any help or advice will be very welcme as the situation is extremely urgent.