Step 1 - Remove your Surface from the Dock if you have one and unplug anything connected to it such as thumb drives or headphones including the power adapter, if one.
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​Step 2 - We need to hard power cycle the Surface. Depending on the type of Surface you have will determine where the power and volume buttons are located. Locate the power and volume + buttons.

Will be along the top left edge of the Surface. Some Surfaces will have the power button on the top edge and the volume button on the left side. 

We only need to locate the power button on a Surface Laptop. It's located in the upper right corner on the keyboard. 

Step 3 - If you've got a Surface with a volume button, press and hold the power button and volume up button, at the same time for 30 seconds. If you're on a Surface Laptop, simply push just the power button for 30 seconds. Ideally, something should happen before the 30 seconds are over, but if you're still at a black screen release the power and volume buttons, and then normal press the power button to see if it turns on. 

Note - You can try this process with the power adapter connected in step 1 to see if any better results

Note - You may get taken to a screen that looks similar to the screenshot below. If you do, tap the exit button on the left, then tap restart now. It should then reboot and take you to Windows.