(adsbygoogle = window.adsbygoogle || []).push({}); i jalibroke my iPhone 4 and it worked fine but when i rebooted it, it loads the apple logo then gets stuck on the pinwheel, what is the problem??????

it means the jailbreak is tethered

if you want the device to be able to boot by itself (without the use of a pc/mac) you need an untethered jailbreak
the latest version of redsn0w can do that

u need to boot while connected to computer. u can use redsnow or this other one if u jailbroke with snowbreeze. i forget what its called...