Have you tried couch to 5k? It's a really gentle introduction to starting to run. I'm around 240lbs, and I run some ridiculously slow 5ks. I wouldn't say I was any 'good' at it yet, but it can feel like such an achievement. Every time you get out there and do something active, you are doing something good for your health, so even if you start of just with some brisk walking, you should be proud of yourself.