Does "The disk is still showing that there is data on it" mean that when you right-click on the burner's drive icon and choose Properties, you get reasonable displays of capacity, etc.? Was the disc formatted to MRW (Mt. Rainier) or non-MRW (UDF 1.50)? Have you changed hardware or software recently?
You could try to read your disc on another computer, possibly after installing EasyWriteReader 188.8.131.52; see the instructions in this thread: http://www.cdrinfo.com/forum/topic.asp?TOPIC_ID=10507
This thread also gives links to CD recovery software; ISO Buster might be a good choice.