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). Disconnect all the USB and DP cables. 

3). Plug the USB 3.0 (the blue one) while the 3 buttons are pressed, and the LED turns white. 

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

5). For another 8s, release the button in the middle, still blue light

6). 1s later, release the last button, and the LED should start flashing.