Background info: Clean install of Ubuntu 18.04 LTS on single partition (SHA-1 checksum verified), Hardware: HP dc7800p, BIOS: 786F1 v01.32. Ubuntu works fine when started but logging into it can take more than 5 attempts. I have applied all updates in the hope that it would fix it, but to no avail.
I have 2 different login problems:
1 - I have the same problem as mentionned by Einnerlink, namely an empty purple screen. My "solution" to this is either to reboot, when the system lets me do it, or switch my computer off and retry from sratch. It eventually succeeds!!
2 - The 2nd problem occurs is that the login screen appears correctly but it denies me access to my account as if I had entered an incorrect password, and it shows a message of the type "internal error". After repeating the loging procedure several times, I eventually succeed.
Is there a fix for this or should I just redo the install!? Thank you in advance for your comments.