Remove the device, and look for obstructions. Most devices, internal to a computer, can't withstand much physical stress, and will break under pressure. Many computers are designed with release levers that need to be opened before a device is installed. Look for these. Install all screws provided with the equipment.
Devices come with a certain number of mounting screws for a reason.
Some devices have moving parts that can cause vibrations that will loosen screws, and eventually cause them to fall out. Using all the mounting screws will reduce the amount of vibration, which in turn will reduce the chance of the screws working themselves loose. If you tighten screws too tight, then you might strip the inside of the screw hole. This can result in fine metal shards falling onto active electronic components causing potentially serious problems. When installing multiple screws into a single device like a CD-ROM, insert all the screws before you tighten any of them.