A hard drive can go bad quickly, but most of the time it fades out over time. One surefire sign of a drive going bad mechanically is a clicking sound or other noticeable noises that are out of the ordinary and loud. Other less obvious signs might be general system sluggishness and unexpected failures with programs or even simple tasks.
To check your drive for errors, there are a variety of tools available.
You can also use windows scandisk by right-clicking on the drive letter in My Computer and clicking on ‘Properties’. Then click on the ‘Tools’ tab and click on ‘Check Now’ in the ‘Error-checking’ box.
As always, make sure to keep a backup (or two) of all your important data!