Start by turning the computer off. Get a medium-size or large paper clip and straighten the long leg. Look closely at the front of the CD drive; you should find a hole that’s about the right size for the paper clip. (Not the earphone jack, of course!) Sometimes there’s a groove just below the drive door instead of a hole.

Carefully push the paper clip straight into the hole to release the catch. The drive door should open without too much pressure. If this doesn’t work, the drive may be physically jammed shut. In that case you’ll need a hardware technician to fix it.