How do I get my computer to reboot when it crashes when it tries to wake up? I have a 2013 MacBook Air and it won't wake up from sleep. Worse, it won't let me hold down the power button to force it to power off so I can just cold boot. It just shows a black screen when I open it, and when I hold down the power button, it just goes back to sleep. Then when I wake it, it shows a black screen again, repeat step 1.

How can I use my computer again??
Regardless of the state of the Mac, holding down the power button will always kill it and allow you to cold boot. Make sure you're holding the power button down long enough—hold it down longer than you think is necessary.