Why can't my computer get past the booting screen?

My computer was functioning normally for me, as my computer always runs out of charge quickly, and my friends suggested a NVRAM reset thinking that it would help with the battery (as my battery only had about 3 Hours left with 100%). I looked up how to do the reset, I think I followed the instructions wrong, now my computer (MacBook Air) when I turn it on it makes the boot up sound and the apple logo appears and the bar begins to load... But really slowly, until around the middle it just stops and it just turns off. I've tried turning it on again and again same thing... Please can some help me?

Thanks Kevin