How do I crash my computer?

On a Windows system:

1. Open up notepad
2. Type %0|%0
3. Save the file to your desktop as anything.bat
4. Double click the file on your desktop

This is known as a ‘fork bomb’. It will open more and more copies of itself, and those copies will open yet more copies. Your computer will be unusable within a couple of seconds after clicking the file and it will crash completely within a minute or two. Once you turn it back on it will be back to normal.

Edit: If you want to make it permanent, then add it to the Startup folder or:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

In the registry using RegEdit.exe

This will run every time you log in. Hence you'll just get into a cycle of iterating crash, reboot, crash, reboot etc.