Data protection on HDD: trying to sort out relevant technologies
Theres one thing that is free to use and works with all modern operating systems: TrueCrypt
It can encrypt your whole HDD which offers a password entry box when starting your computer. The encryption is completely secure, you can choose the algorithm to use (or multiple algorithms). Also the encryption is pretty fast. If you benchmark with and without you will see some overhead, but if your processor is strong enough (which it should be, since it's an i5/7) you will not notice it.