Could be the first signs of numerous problems, but the first step is generally the same in every case. Make sure your backups are up to date.

If the drive is in the early stages of going out, you'll want backups. If it's a virus or some kind of malware, you'll want backups if it takes the system down with it. If it's filesystem corruption that's gradually progressing, you'll want backups before it makes things irretrievable.

So, get with the making sure your backups are current while others postulate on possible causes.