Hello and Welcome to Tom's Hardware,
Please tell us more about your computer, the OS, HDD's other attached devices, and if any recent program installations, updates, reg cleaners, power outage, that were used or occurred that might have caused a problem.
Also do 2 things:
Go to Disk Management and in the lower graphical area please list what it says in the Disk Status column, like Disk 0, Basic, Size, Online or whatever, and in the Volume Status column to the right below the dark blue color band, what it says, about the different Partitions, Volume, DriveLetter if there, Size, NTFS, Healthy, any other info.
Next start the Command interpreter (cmd) and carefully type "DiskPart". You will get DiskPart> as it starts the disk partition interpreter.
Then type "List Disk". Please write down the printout.
Then type "List Volume". Please write down the printout of all the Volume recognized, for us to review.
Then at the DiskPart > type "Exit" to exit the DiskPart interpreter, then "Exit" to exit the Cmd interpreter.
That way we can best figure out what's going on..