When the headset is disconnected, you could enter the DFU mode manually, here are the steps:

1). Stop the service PiserviceLauncher from Task Manager. In some cases, you may need to start the service and then stop it to make sure that Pitool gives you an error of 30000.  


2)Unplug the power adapter

3)Plug the power adapter while the 3 buttons are pressed, the LED turns white.

4)Count 8s, release the power button, the LED turns blue

5)Another 8s, release the button in the middle, still blue light

6)1s later, release the last button, the LED should start flashing red/blue/green.