One particular problem is redsn0w hangs after you followed the instructions to put the iPhone into DFU mode and it keeps showing “Waiting for Reboot” message.

But there is a simple solution for that:

Simply unplug the USB connector from the iPhone and plug it back again. Right after that, you’ll notice a momentarily refresh on the screen. Then everything should go fine afterward.

The solution has been tested on Mac with Redsn0w 0.8. Hopefully, it will also work on Windows.