We’ve gotten a lot of feedback from users who can’t launch a DFU ramdisk because their iPhone home/power buttons are broken or intermittent. We’ve added a new redsn0w feature that lets you enter DFU mode as long as your phone is healthy enough to restore to a normal, everyday IPSW. You don’t need to be already jailbroken to use this method.
How to Put Into DFU Mode With Broken Home / Power Buttons
In redsn0w, go to “Extras->Even More>DFU IPSW” and select an IPSW that is currently being signed for your device and that you’d normally be able to restore to without any hacks. redsn0w will create an “ENTER_DFU_” version of the IPSW that you can restore to just like any other IPSW, except that now you’ll be dumped into DFU mode towards the end of the restore
WARNING : your screen will remain completely black.The only way to even know its on is that iTunes and redsn0w will detect it!.
Here are the download links.