I have a 4 years' old Compaq PC with OEM CD-Rom, and have recently got a DVD/CD-RW combo drive. So far, no problem.

I have been burning Sony CD-Rs through Nero (mostly data back-ups, and some music), and can access the files either from the old CD-Rom or from the new combo drive. Even other CDs (e.g., third party music, or from books) open in either drive.

I have just bought Sprint CD-Rs, and after burning data files find the CD is opening in the combo drive, but not in the old CD-Rom. In fact, the old CD-Rom is not recognising this CD.

What can be wrong please?
Thanks,

It's likely that these new CD-R are a very poor quality & the quality of the burn is too poor for the CD-ROM to read.
Try these on another computer & see if that one has the same problem.