A problem with graphics on Ubuntu 18.04

i have just tried to find help in ask ubuntu , also on linux italy official telegram
they noted me to ask at assistance nvidia for resolve thisa problem.

is all written in the first link that i pasted here but in 2 words i cant instal nvidia driver-340

after installed the driver , after rebooted , i have another problem, when i try to reboot i cant see the ubuntu logo but only the lights that are going from left to right up there are 2 commands that are : /dev/sda1: recovering journal /dev/sda1: clean, 205561/61054976 files , 7567449/244190208 blocks and remain in loop i say thank you and i hope that somebody can help me , if you need other information is not a problem.