Can a failing hard drive cause a 'c00021a' error?

Yes, a failing hard drive is a common cause. As the drive degrades, files can become corrupted, leading to the 'c00021a' error. Signs of a failing hard drive include slow performance, frequent crashes, and unusual noises (clicking, grinding). Run a disk check using `chkdsk` to identify and potentially repair errors, although a failing drive may not be repairable.