I started to install Lubuntu 18 (a variant of Ubunutu) but the window graphics became corrupted after I selected the language. This is a known bug that sometimes occurs and there are various suggestions to workaround the problem. What worked for me?
- Press Ctrl+Alt+F1
- Press Ctrl+Alt+F7
- Press Ctrl+Alt+F1
The screen went to a black blinking cursor and then back to normal.
Good luck!