Maybe you can advertise around campus or online in your area to let people know through friends since they're your main word of mouth connections that you are now offering tech services for a basic fee. You can sell them on this by offering additional services such as virus checks, software updates, etc. As long as it's not too much out of their price range, they'll consider paying. It's nice of you to do it for free but to be doing all that work and no pay isn't fair to you.