Data Recovery from CD

A guy I work with backed up his hard drive to CD and now there are problems accessing his data. I wasn't there when he did this so I don't know any of the specifics. Everything can be viewed in Explorer, a very small quantity of files can be opened, but most can't. It was burned to a new CD-R and the surface is not scratched. Attempting to open different types of files would result in different messages....here a few:

Attempting to open a Word document would result in the following;
*The document name or path is not valid

Access;
*Invalid Argument

.exe file;
*Not a valid Win32 application.

Any suggestions on how to recover this data? Perhaps a data-recovery tool for CDs? Thanks.

 

I should correct how I stated that, he backed up some files from his hard drive to CD, not the entire hard drive.