At a risk of sounding unintentionally patronising, 21 is still very young to be deciding what the rest of your life will be like. Obviously suicide at any age is a tragedy but I always feel an extra pull of sadness when someone so young is comtemplating ending it all or even just resigning to a destructive or empty life. A huge amount can change in one year never mind five or ten, and at 21 you are still wrestling with becoming adult which is hard for anyone even with a healthy background (assuming yours isn't).

I'm in my thirties and my life has changed radically from my largely suicidal late teens and early twenties. It certainly isn't a picnic (external factors) but I don't feel like I'm going to kill myself anymore. Life can change/get easier if you give it a chance. You never know how you'll feel a few years down the line. At times like this I do think it's important to try and remember situations/feelings are temporary, no matter how all emcompassing they feel at the time.

Like Perna said, start with an interest, however basic. I don't think we need to achieve much to have a good life. Just find something worthwhile, no matter how small. Take it from there. You never know what's around the corner.