I cannot install, copy or create images for some of my games

Do you provide solutions copying, ripping, burning issues with cd/dvd games. I have tried to make backups of some of my game cd’s and dvd’s as a security measure in case of any mishaps. This sometimes works but at other times doesn’t. I would like to know what might really be causing this and if there is any software or hardware or software solution’s available. I recently lost one of these dvd which was not copied. Here are some specific questions.
Another problem occurs when I download legitimate games from pay sites on the net. As image files they run well but when I back them up on cd’s they wont install. Could you help?