Take it out, remove the top and clean the round drive hubs above and below the CD tray. When they get dirty the drive can't spin the disk, and can't read it. When this happens the light stays on or blinks as you described.
Clean the drive hubs with rubbing alcohol and Q-Tips, and let it dry for an hour or so before reinstalling. don't touch the laser lens or pour alcohol into the drive...You can lightly brush off the laser lens with a soft clean brush, like a cosmetics brush, but be very careful, one scratch and you're going shopping...
If you had everything...Where would you put it?
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