Make sure your PC speakers are turned up so that you can hear them. Make sure your phone is turned on and connect it to the PC. You'll hear the device connect sound. Now, hold in both buttons...power and home. Hold them for about 10 seconds and you'll hear the device disconnect sound. As soon as you hear it release only the power button. Do not let go of the home button. After 5-10 seconds, you should hear the device connect sound again. Let go of the home button and you are in DFU. There will be nothing on the screen, but iTunes will pick up the phone in recovery mode."