Okay so after I jailbreaked my iPhone everything was okay but now each time I turn it on it shows me the apple sign then turn off by it self what to do plz help !!!
What has happened is that you've performed a Tethered Jailbreak. Every time you restart your iPhone now, you're going to have to plug it into your computer, launch redsn0w and select "Just boot tethered for now". For more, see the source.