Excel file produced on Windows XP will not open on Windows 7

Why is it that my excel files which, are produced on my WINDOWS XP lap top, will not open on another lap top which has WINDOWS 7

Few things to look out for:
1. do you get an error message, or does nothing happen?
2. do the excel files have an excel icon?
- If not then they may not be linked to excel as a default program so you'll have to right click on the file, open with... choose excel and make sure the button for always open with this program is checked.
3. If this is a new Win7 laptop, are you sure MS office is installed? Sounds basic, but must check everything. (also a lot of new machines don't come pre-installed with office anymore)