CD or DVD it is formatted as a data disk. There are a couple of fairly obvious reasons why it cannot be read on your Mac...
- The disc uses a file format your Mac does not recognize or
- Due to variations in the dye used in the disc media and variations in the frequency and strength of the read laser in your drive, it cannot read the disc.
Since you have access to a PC that can read the disc, either could be solved by copying the disc contents to the PC then burning a new disc on a new blank using a file format you know the Mac can read preferably NTFS.
