I advise you to back up your data from time to time before it is too late. You wouldn’t have to go trough recovery procedures if you have your data copied somewhere else. But if you don’t have backup don’t panic. There are ways to retrieve precious files. I will go through some essential things when it goes to data recovery.
Try to set up disk on another computer
You can’t boot your system. You can first try to set up your hard drive on another computer. Maybe some system files are corrupted and you can’t boot operating system but your other files are ok and can be accessed via other operating system. If everything is ok your drive will show up in my computer like normal drive or partition. Grab most important data first because this is risky process and your drive may stop working any time. When you do that you can try to copy whole data structure to other disk and slowly select and categorize old data.
Try some mechanic things
Maybe the files are ok but some mechanical part of hard disk is dying. Try some basic things like reorienting drive. If it was classic desktop laying flat try to switch it to side or even standing up. This can work in some cases. If it heats up a lot try pointing fan to it and the things can get better. If heating is not the problem and disk is on power source but you don’t hear a thing from it try to gently hit it on the table. The disk may be stuck and needs a shake to continue working.
Try to replace electronics
Every disk consists of electronic parts and mechanical parts. Mechanics is may be ok but in some cases electronics is the reason of broken drive. You have to buy same model (new or used) unscrew the board and replace with working drive.