There are three possible problems:

  • ROM (cd/dvd reader) device does not work properly (e.g. pin does not read the disc or ROM is full of dust …)
  • CD/DVD disk you are using isn’t valid (e.g. scratched/damaged disk …)
  • PSU’s cable which grants power supply to ROM device might be incorrectly (e.g. does not assign the correct or balanced [I’m not sure what’s the right word in English] power)

It should investigate by yourself what the problem might be.