Disc problem

I made a photo disc on my old PC and they used to work on my mac but now when i insert them nothing happens.
My computer recognizes that there is a disc and even gets the name but when i click on the disc image it says that there is nothing on the disc but when i open it in Toast it says the disc is full,whats going on can anyone tell me.
As usual any help would be greatly appreciated.
thnaks Scott