Windows 7 Can't Locate Files On An External HD

For 5 years I had good service from an orange top Toshiba laptop but have now upgraded to brand spanking new black top Toshiba laptop ... Oh, you need the technical stuff as well!

-Old: Toshiba Satellite M50 series (Windows XP Home/MS Office 2003 Pro).
-New: Toshiba Satellite M745 (Windows 7/MS Office 2010 Pro)
-Migration of data: Seagate external hard drive.

I have religiously backed up all data files on a routine basis and checked for function and accuracy before disposing of the trusty orange M50.I now have the sleek black M745 up and running and with the exception that I can't get my head around the differences between MS Office 2003 and 2010, all seems to be well apart from one particularly nasty 'showstopper'.The new laptop can't open any of the files, MS or otherwise, stored on the external HD. Although I can see the files on the HD and am told that there is data in the files, I get the message that the file path cannot be found.The vast majority of these files are MS Office documents, power-point files and Access databases (created in MS Office 2003). However, movie files also receive the same message.