Install ADT driver:

  1. Open PC settings
  2. Under General, look for the item Advanced startup at the bottom and click on Restart now.
  3. Now select Troubleshooting and click on Advanced options in the next window.
  4. Now click on Start settings and then click on Restart.
  5. A restart is carried out in the start settings. Here you can use the F7 key to select the entry Force disable driver signature.
  6. Once the PC has been started, simply attach the Android device of your choice and install the drivers.
  7. This start setting is only valid until the next restart is carried out.
  8. Install drivers e.g. for Nexus 4 and for Nexus 7 or see manufacturer's pages