Office 2007 to 2010 problems

I just purchased a new laptop and have been moving my files from my old machine with VISTA and Office 2007 to the new machine with Windows 7 and Office 2010.

I installed Office 2010 and it all worked fine, when I moved my saved files over to the new machine I could not open Excel files. I finally got that fixed and everything opens fine on the new computer.

When I back up the new computer on an external drive I am unable to open the Excel files again on the external drive or even if I move them back on the new machine, the same files currently on the new machine [in a different folder] open fine.

How do I go about getting a backup copy on an external souce that can be read by another computer?

Thanks!

I wanted to add that I am able to open the files through an open Excel document by browsing for them, just not through windows explorer.

Update

I tried something that seemed to work.

I opened each Excel document on my computer and entered one letter into an empty space, and then deleted it [simulating a change], when I closed the document it asked me if I wanted to save the changes and I said yes. Then when I move them to the backup drive they worked fine. If I did not make the simulated change and save they would not open on the backup drive.

Just making the document ask if you want to save changes evidently makes it work, even if you don’t make any real changes.

I tried the same thing backing up on my flash drive and it worked there also, no simulated change and they will not open, simulate a change and they work fine.

Any new Excel documents I create on my new computer back up fine.

try re-associating the .xls/.xlsx files back to their appropriate program by righ clicking/open with/insert office version here

I had tried that but it did not work.