black screen boot

[Mireia Grau]

I have just install Ubuntu 20.04 in a pc with Windows 10. I have used an usb stick. Before the welcome window emerged the screen went black with white letters completely frozen. Then I pressed the power button (one or two quick presses) ans suddenly the welcome window emerged. All the installation seemed to be fine. But when I restarted and I have chosen "Ubuntu" in the first menu that has appeared when I started the computer (I could choose between "Ubuntu", "Advanced Ubuntu", "Windows" and "UFI Firmware") and then the screen went mostly black with purple and green lines. Then I pressed the power button to quit (two quick presses) and suddenly I could have access to my account and then everything was normal. I have tried many times and always it's the same. I also have found another way to skip the black-green-purple screen going to "Advanced Ubuntu", then "Ubuntu recovery" and then "normal boot". If I do it this way everything seems fine and I skip the frozen blac-green-purple screen. What should I do to fix it?

So sorry if is confusing, I'm new in all of that and my English isn't good. Thanks very much.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
Uname: Linux 5.4.0-26-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Wed May 6 13:53:28 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash nomodeset ---
InstallationDate: Installed on 2020-05-06 (0 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=es_ES.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
Symptom: installation
UpgradeStatus: No upgrade log present (probably fresh install)

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. Reviewing your log files attached to this bug report it seems that there is a problem with your installation media (CD/DVD). You can verify the integrity of the Ubuntu ISO files you downloaded by following the instructions at https://help.ubuntu.com/community/HowToMD5SUM. You might also retry your installation with new media. In the event that is is not in fact an error with your installation media please set the bug's status back to New. Thanks and good luck!

[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]

[Launchpad Janitor (janitor)]

[Expired for ubiquity (Ubuntu) because there has been no activity for 60 days.]