Maybe it has been so long since you've really cared about something that it feels like you've lost the ability. But no matter how deep your feelings of caring are buried, they're in there somewhere, and it's time to uncover them. To care is to "feel concern or interest; attach importance to something," to "feel affection or liking." By that definition, who and what do you care about? Make a list of anything that causes you to feel interest, concern, or attachment of any kind.
Write down the names of people you feel attachment to—parents, siblings, friends, and anyone else who has a pull on your heart. If you think about the person often, and you'd miss them if they weren't there, you probably care about them. You don't have to love or even like them to care. By the same measure, write down things besides people you care about. Don't write down the things you should care about, just the things you actually do. Maybe your life is better because you play soccer, or you can't imagine a world without Warcraft. Maybe you care about poetry, or you love a certain movie star. There's no limit to how long your list can be—write it all down, big and small. Be honest with yourself as you make your list, and don't leave anything out. Maybe you've been conditioned to act like you're "above it all," or to hide the things that make you tick. People will try to tell you what you should and shouldn't care about, but you'll have to learn to ignore them for the sake of your own happiness. And in most cases, sticking to your guns and expressing that you care will eventually win you others' admiration.