Your hard disk, whether mechanical or solid-state (an SSD), holds all the files on your computer. Without it, the PC won't start up. Hard disks do sometimes fail, in which case you'll need to buy and fit a replacement. And, of course, copy all your programs and data onto it. Plus Windows itself. Which is why it's always sensible to keep good backups.
Modern hard disks use something called Self-Monitoring, Analysis and Reporting Technology, or SMART for short. It means that the drive regularly checks itself for possible errors and reports these to the operating system. By checking the status of your SMART data occasionally, you can find out whether your drive is at increased risk of failure. And, if it is, you can take extra steps to ensure you have backups and a replacement drive available.
Although there are plenty of free programs around that will report on your drives' SMART status, you can actually do it directly from Windows without the need to download or install anything. To do this, just open a command prompt by searching for the CMD.EXE program or the Command Prompt utility. Right-click it and choose Run As Administrator. You'll then be presented with a black screen into which you can type commands.
To check your drive status, the command you need is:
WMIC DISKDRIVE GET MODEL,STATUS
Press Return after typing the command. This will show you the model number and status of each physical drive in your system. Assuming the status is OK, then the drive is fine. Otherwise, look up the details of the status in your favourite search engine to find out more about the problems that are reported.
To exit the command prompt, type EXIT and press Return.