What happens if I open the hard drive cover?

Opening the hard drive will not only void the manufacturer warranty, it also can cause losing your data permanently. In other words, it's a bad and unwise thing to do that render irreparable harm to device and digital information in it. The clean room laboratory operates in specifically air-controlled environment to prevent contamination of the crystal clean and smooth data disks from the contact with any contaminant air-born particles.

A single tiny speck of dust could cause the devastating effect for data integrity since any mechanical contact with the moving part of drive (the drive's heads) will scratch the disk surface coated with the magnetic layer of the digital information. Even if some part of your data can possibly survived after such unauthorized intrusion into storage device, it will cause a big deal of problem for data restoration specialist to work with the tampered drive and make the recovery more costly and complex.

When hard drive is open in uncontrolled environment its internal disk platters exposed to airborne substances. Surface contamination is the main factor affecting quality and quantity of recoverable files. This particular laptop hard drive has a platter (disk) made from glass and was coated with the thin magnetic layers for storing information on both sides. Even a little amount of invisible dust can initiate a catastrophic process of self-destruction. The reading/writing needle-heads, instead of flying over rotating platter, will start bumping over the dirty, contaminated disk’s surface, scratching and scrapping it to the very glass substrate. You can notice practically clear platter on the picture - clear from data. And literally clear (transparent) glass allows to see even few mechanical parts under the disk, including a lower magnet for the actuator.