If the phone won't boot at all, try a new battery. Then try a jig. Then find Hopper8's 'Odin troubleshooting' guide stickied in General & try the 'jump start' method. Then take it to a Samsung service centre or local mobile repair shop.
Not a lot beyond that anyone here can suggest if the phone won't even boot.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?