If you are having a problem with getting power to your CD/DVD drives, I wouls suggest that your best bet would be to see if your PSU is malfunctioning/overloaded. If no power is getting to the drives then the BIOS will not be able to see them. It sounds like this is an intermittent fault, so why not remove the power cables to CD/DVD drives then power up your PC & see if everything works OK. If all is well after a while testing, then power down PC & re-attach a power cable to ONE of your CD/DVD drives, restart & test again. keep going in this order & see if the fault re-appears at any stage.