How to resolve the issue of Ubuntu not being able to turn on after the screen is closed.

If the screen cannot be reopened after turning it off in the Ubuntu system, you can try the following solutions:

1. Try pressing any key on the keyboard or moving the mouse to see if you can wake up the screen.
2. Try pressing the power button once to see if you can wake up the screen again.
3. Pressing the Ctrl + Alt + F1 key combination to enter the TTY terminal interface, then press Ctrl + Alt + F7 to return to the graphical interface to see if the screen can be awakened.
4. Press the Ctrl + Alt + Del combination keys to attempt to restart the computer.
5. If the above methods do not solve the problem, it may be due to some malfunction in the system or driver issues, you can try restarting the computer or rebooting the X window system.

If the above methods still cannot solve the problem, it is recommended to check the system logs for any related error messages, or try seeking help on the Ubuntu official forum or community.