Try this... If you've been docking your SP3 with the Surface Type Keyboard:
1. SP3 up and running
2. Remove the keyboard
3. Dock
4. Search charm, search for "Devices and Printers"
5. Click "Add a device" to make sure all devices are detected
6. Check for Windows Updates
7. Try a shut down and restart while docked.
I wonder if your device is trying to boot to a device not installed. Check your boot order:
From power off
1. Hold down Volume Up button
2. Press and release power button - keep holding Volume Up
3. When "Surface" logo appears on the screen, release the Volume Up button
4. Check/change the boot order setting