Volume Repair

I've been getting a message on my Onyx saying "the volume needs to be repaired." I started my mac using the install disk and going to disk utility to repair it but it did not work. I then installed "Apple Jack," but that didn't repair it either. I'm not sure what else to do or what it could be. My computer is running very slow, it becomes unresponsive and I have to turn it off. Sometimes on start up it takes 10 to 15 minutes. My mac is a 10.5.8 Leopard. Does anyone know how to fix this or have an idea of what the problem is? Thank for the help.