If you don't have Bitlocker enabled then you can remove the hard drive and connect it to a computer you can log in to. You can then browse the drive and copy the files you want. If you do have Bitlocker enabled and don't have the recovery key, then your files are lost.

To erase the drives, you can either:
1. Format the drive when it is connected to another computer, which will of course also require reinstalling Windows in order to be able to use it again.
2. If you have Windows 10 you can boot into recovery mode (usually by pressing Esc or F11 at boot up) and there should be an option to restore to factory settings, which will give you a fresh-out-of-the-box install of Windows.