Another way you may lose data is because you deleted something, or formatted a drive that had something you need to recover. Data recovery software can often be used for this purpose, and many things can be recovered. Perhaps a different article someday.
Sometimes, especially if the drive has been dropped, the drive case has to be opened, and the read-write heads have to be re-aligned or replaced in order to recover the data stored on the drive. When all else fails, or if the drive will not spin, the drive will be disassembled, a new drive of the same model is also disassembled, and the platters that have the lost data are installed into the new drive housing in order to recover the data.
Remove the unbootable disk from the computer, then connect it to a external USB host SATA adapter(or directly to a SATA port on the mainboard) and mount it over another computer that is booting correctly. It doesn't matter if your unbootable Windows was protected by a boot password (it will matter if your disk was protected by Windows encription). If the partitions and the disk were not damaged then you be able to mount it on your Windows(or even Linux) system and recover all your "lost" data.