I have a brand new laptop:
Lenovo Legion Y540 Memory: 16GB i7 2.6GHz 500GB
I deleted Windows and installed Ubuntu 18.04.3 LTS, which I have on a pen drive.
sudo apt-get update
works fine and when rebooting, Ubuntu starts fine.
However, after running
sudo apt-get upgrade
and rebooting, Ubuntu does not start.
After the Lenovo start screen, the screen freezes with a black screen and a greenish/purplish horizontal line across the top of the screen. At this point, I have to force a shut down by holding the on-off button and reinstall Ubuntu.
I didn't do anything else on the laptop, and I did this quite a few times now, with reliable results.
What should I do?