There can be several reasons for a black screen, here are some common solutions:
1. Check whether the power cord and video cable are secure. Sometimes a loose or disconnected cable can cause a black screen.
2. Check whether the graphics card driver is installed correctly. If the graphics card driver is not installed correctly, it may cause a black screen. You can log in using the command line (Ctrl + Alt + F1) and try reinstalling the graphics driver.
3. Check whether there is an update for the Ubuntu system. Sometimes a system update might fix some black screen issues. You can try to update your system with the following commands in the command line:
sudo apt-get update
sudo apt-get upgrade
4. If you encounter a black screen after logging in, it may be because of a problem with the system login manager. You could try switching to tty mode and reinstalling the login manager.
You can switch to tty mode with: Ctrl + Alt + F1
5. If you are using the Ubuntu desktop environment, there may be some desktop environment specific issues. You can try switching to Ubuntu's default desktop environment (GNOME) or another desktop environment.
6. The last one, if it is a wireless connection system, it is most likely to be a network problem. For example, a smart car is equipped with an Ubuntu system, but it is connected to its own computer nomachine through a LAN. If it enters a black screen, it may be a network problem and the connection is unstable.
Finally, if none of the above methods work, you can try to reinstall the Ubuntu system. Before reinstalling, you can back up your personal data to an external storage device to avoid data loss.