I bought a jailbroken iPhone and it shut off and I can no longer use it?

I did it initially jailbreak it, so I don't know how to unjailbreak it. It's jailbroken with redsnow and cydia. I just don't know how to get into the phone. It stays on the apple logo.

Chances are the phones is done for, there's no way to unjailbreak a phone which irks, but the newer the smartphone the more impossible it is to jailbreak

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