Stuck in soft DFU mode
Solution 1:
Use ReiBoot app to push the phone out of recovery mode cycle. I had the same problem and only one that app solved it. I tried going into DFU mode and without DFU mode, using .ipsw files to restore old and new iOS version, and none worked. I installed ReiBoot and in 5 minutes I solved the problem. Just install the app for mac (I do not know if it works for windows) and plug the iPhone in the computer. Open the ReiBoot and push the phone out of recovery mode cycle. VOILA! This was the only thing that worked for me. Nothing else worked. I tried different USB ports, different USB cables, nothing else worked, literally.
Solution 2:
Found the weird but working way,
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On another machine, connect i-device to iTunes. It will be detected as if in "Recovery Mode"
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Download IPSW for your device that is still signed
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Download Redsn0w, Go to extras -> even more extras -> DFU IPSW. Open original IPSW, let the tool create a patched IPCW
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Back to iTunes - push ALT and press the "Restore phone" button. In the undocumented menu, open patched IPSW.
You'll go
Soft DFU -> Recovery -> DFU -
Back to Redsn0w. Extras -> Just boot