With what
It completely depends on the gun and the problem. N-Strike is a line of guns, not a particular one.
you pull the pump out and jam or hit it back in hard enough repeatedly until you feel air in it or its harder to pump
why what is wrong with it
i have no clue how to fix it because i dont have one, but you probaly left it pumped for a long time, which can break it.
destroy it with a sledgehammer
If you mean to mod it, check out this guidehttp://modworks.blogspot.com/2009/09/nerf-raider-mod-guide.html
Don't mod. modding can be dangerous and get you in trouble. ESPECIALLY don't mod the darts with tacks!
You probably can't. If it stops working, it is broken.
it depends on whats broken. open it up and take a look. is something is broken odds are you can fix it by reenforcing it with glue and wire
You can use WINE.
You don't hahahahah fooool
go to nerfhaven.com, go to the search engine, type in firefly mod, and have fun.