Recently I upgraded the memory from 1GB to 4 GB and then I also upgraded the OS X to Yosemite. Since my computer continues to shut off on it's own now, I want to revert back to an early version of OS X than Yosemite. To do that I have read that I need to reboot using the original installation disk. But when I try, nothing happens. The computer doesn't seem to be able to read the disk. I can hear it trying to read the DVD disk unsuccessfully and then finally the DVD disk just ejects.
How can I revert to an earlier version of OS X than Yosemite?
How can I revert to an earlier version of OS X than Yosemite?