I have seen a few laptops recently that have started encrypting their drives – using BitLocker – once the Windows setup process is complete. Whilst this is a great security feature it may not always be required (if you use an alternate encryption method for example). There is a simple command to turn off / disable BitLocker via PowerShell. Firstly, run PowerShell as Admin, then enter:
manage-bde -off C:
[NOTE: Replace C: with the drive that is (being) encrypted of course!]