RadioHans: I concur with the simplicity of copying all the data to another medium. DVD/s or an External Hard Drive or an Internet Hard Drive in a case with a USB plug and play cord. Once you have all that data onto another medium, then reformat the hard drive as mentioned in NTFS Format.
If you have the software, you would actually want to delete the partition, then format the Hard Drive. Use a label of your liking and do not assign a drive letter to it. Call it: Main, Storage, Backup, Media etc. Whatever you like. Once it's back in the computer for whatever use, the system will assign it a correct letter on boot-up. You can always change that letter if it is not going to be used as the C-Drive. Here is an example of my two 500 GB HDD/s. C and D .
Having a second Internal HDD for creating an Image Backup of your main hard drive on a regular basis is fast and easy. And--if your main hard drive starts to go bad, you can copy the media from the backup hard drive to DVD/s or an External Hard Drive and Clone the C-Drive to your Backup Drive. Then off to an online store to buy a new Backup Hard Drive for about $50.00 USD.