[EDIT] I reached to boot the 14.04.5 stick using the following sequence :
ESC->choose language with arrows keys->Enter->F6->down key to nomodeset, hit space bar, ESC, TAB, type nomodeset at the very end of the boot options line, just here where the cursor now shows -> Enter
[EDIT] I reached to boot the 14.04.5 stick using the following sequence : >F6->down key to nomodeset, hit space bar, ESC, TAB, type nomodeset at the very end of the boot options line, just here where the cursor now shows -> Enter
ESC->choose language with arrows keys->Enter-