this one is easy, make sure you have sound on your pc so you can hear the usb actions, hold down power and home until you hear the ipod usb noise on pc, this should now mean the ipod is switched off, then hold down power and home for 10 seconds then let go of power button and keep home pressed in until ipod usb noise happens again, or just leave itunes running then you will see when it is connected for a restore again. I just had this problem too, It got halfway through the jailbreak, said something like, flashing nor, and the screen went blank, just trying again now