You also need to look at how you think about yourself. Whenever you think "I can't because of x, y and z" you need to stop yourself and ask yourself what made you think that. Is it something that happened a long time ago? Well, in that case, it isn't relevant, and you need to tell yourself that actually, that's not correct anymore, and you can have a go at doing whatever it is. If you never try, you'll never know, and while it's far safer to not try, you won't help your self-esteem if you never try, as by not trying, you continue to perpetuate the "I'm useless, I can't even do this" cycle and make yourself feel worse.
It's not easy to do this. Talk to your friends, and tell them that you're trying to combat this, but that you'll need their help and support.
Even now, I'm still not very good at accepting compliments, but I'm far less hard on myself than I used to be.