After successfully using a Windows 8.1 eight-drive parity Storage Spaces pool for about a year, I decided to back-up my data, delete the pool and start over with additional drives.  When I went to create my new Storage Spaces pool, it would accept the the new drives but refused to accept the old drives, stating something to the effect that they could not be added to the pool because they were in use.  Storage Spaces shows NO storage pools in effect.  The drives are totally empty and work perfectly as regular data drives under Windows 8.1.  But I cannot get them to become a part of a new storage pool under Storage Spaces.  How do I clear either the drives or the Windows 8.1 registry so that these drives are not seen as currently in use?

Try using Reset-PhysicalDisk -FriendlyName "disk name" (powershell)

If you need help to find the disk to get the name use  Get-Physicaldisk