It makes a clicking noise, perhaps even a grinding noise, and then stops. It won't read either NGCD discs nor music CDs. I tried holding down the little switch on the inside that tells the system whether the tray is open, and even poked and prodded the lens with a cotton swab. Any ideas on what I should do now? How can I methodically check off what's wrong until I find out what the problem is, and then fix it?