So last night i wanted to upgrade my HD and i swapped it in. Then placed the snow leopard disc in.. started the boot and it wouldnt boot from the disc. I tried my leopard disc then and it wouldnt read either. So i swapped my old hdd in and booted back into osx and everytime i placed either the snow leopard or leopard disk it would spend some time spinning/reading but then just spit the disc out. Funny thing is that i actually upgraded from leopard to SL using that exact same disc (its not just an upgrade disc) and it booted fine. I tried just a regular dvd/cd in my drive and it loaded right up.. so for some reason now i cant boot those two OSX dvds anymore. What i was gonna do was boot using the disc start installling and then when it asks me use my time machine backup i have on my external to setup my mac as before. Any help guys?