why not try the Encrypter and Decrypter tool of glary utilities.
I heve been using it to keep my personal files confidential. It didn't make my PC running any slower. Oppositely, I think PC runs better due to its maintenance it brought to me. It's free ,small and safe. Here I found the download site for you: http://www.glaryutilities.com
I hope I am helpful to you in this question.
Is there a good encryption program that doesn't slow down the computer BOOTUP or SHUTDOWN????
I use to use Folder Lock but had a problem with that.
By the way, I need to encrypt a folder that is around 10GB.