Your hard disk fails. So what are you planning to do? Maybe you thought that data recovery is a pretty expensive service, so you may try diagnosing your hard disk at home. No way! Data recovery is not a DIY job. In your attempt to fix the disk you may render its data completely useless and you may eliminate any chances of recovery, even from a data recovery company. So before you proceed take a quote from a data recovery company. If you cannot affoard it and you are not afraid about your data, the attempt whatever you read in the internet.
Hard disk platters, heads and motor is not hermetically closed under the hard disk cover. They still breath through a special filter. But what is very important to know is that hard disks are made in such way that no dust is allowed to enter the internal of the disk. One little particle of dust is capable of rendering a disk unrecoverable. The distance between the heads and the platters is so small that a simple particle of dust, if enters this area, will make the heads scratch the platters.
When the disks are opened in data recovery labs, they are opened in special chambers called Clean Rooms or Clean Benches, because they allow no dust. This non polluted by dust, enivironment is established by using equipment that costs thousands of euros to be ceritified for this job.
Below there is a video from Gillware, that shows why nobody should open the cover of the disk.
A technicial will open the disk, just take a look and close it back. The disk is already dead and needs to be seen by an expert.
So if something goes wrong with your hard disk. Ask for a quote and then consider if you would like to experiment with it.