broken iphone3g: re-jailbreak, wipe before repair, help

[PARUSA]

Hi and good day to all, i'm here again to ask for help on my iphone3g.



I wanted to at least wipe or even re-jailbreak it with the same firmware and ios version if possible (note: i upgraded my wife's iphone to 4.2.1 with ipad baseband and i wasn't happy with it, very problematic i may say).

The problem is the phone is partly broken. power button ain't working because it had a big fall, at the same time scratching the screen, i opened the device and tried to fix the button, but unfortunately, damaged the earpiece.

I then asked a repair shop for any solution and the problem could be the board. I just ant to make sure before i send for repair, all things are like new or data and personal files are deleted.

I have backup using itunes.

Now, i can't jailbreak it because i need the power button to enter DFU, right? what's the best way to jailbreak it again, step by step will be very helpful.


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UPDATE:

i tried this -

Choose General > Reset and tap “Erase All Content and Settings.”

* All your information and media are deleted. You must sync iPhone with your computer to restore contacts, songs, videos, and other information and media.

Reset the keyboard dictionary

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anything else?