Lost access to CD

Hi all

Got a feeling that I may be clutching at straws with this one.

As it happens I have been using a CDR to store some Excel data on, the disc as been stored in my office draw and I have been adding data to it over the last twelve months without no problem. Today when I tried to open it the PC was unable to do so and within the properties the used and free space both read zero, the pie diagram indicates that the disc is full though I know that there isn't that much data on there, if anything there's no more than 400kb on there.

Is there any software about that could break into my disk so I can retrieve my data.

Unfortunately like a twonk I never kept anymore copies, a lesson learned

Many thanks in advance