I bought a new computer, a precision tower 7920 with Quadro RTX 4000 GPUs. Because the nvidia driver installation is so complicated, I ordered the machine with Ubuntu (as it was supported by Dell and comes pre-installed).
However from the very first time I turned the computer on it won't boot, getting stuck at
Starting Gnome Display Manager
showing no error messages, but not moving forward from that point. Just like in this question: GUI does not start
It looks like the graphic drivers aren't installed properly. I could start debugging this. But my concern is: Should I even consider that Dell would send a new computer that is incapable of booting? Is this an 'exchange the product' case?
You don't have to accept a computer that doesn't boot from Dell or from anyone. If the computer has a guarantee, return it and make them honor their guarantee. If you do too many things to try to repair this computer, it may be used as an excuse to void the guarantee, and you'll be stuck with a useless unbootable computer.
You could boot off a flash drive and nuke the existing OS installation since it seems to only be a software issue but, as others have said, it is Dell's responsibility and you should file a warranty claim.
In addition to the what everyone else said, there's also the very distinct possibility that there's a hardware problem. Definitely contact Dell.
What did you buy? Some hardware, or a working computer (with the knowledge that Linux is well supported on it)?
What are your skills? Are you fluent enough on Linux to be able to reinstall some Linux distro on your computer without any help? Are you capable of detecting most hardware issues?
How much is your time worth? Can you wait a week to get that problem fixed, or do you prefer to fix it yourself because you actually have some work to do quickly with that computer? You'll probably lose nearly a week (in practice) to get that problem fixed by Dell. Of course, it will be fixed.
The latest Ubuntu is 19.04 now. You might have reasons to prefer the latest distro, not the most stable one (or vice versa). I prefer, as a developer, to have the latest libraries.
I've got the same workstation at work (but right now, in mid-August 2019, I am on vacation) and I preferred to reinstall Debian on it.
We are sadly living in a world where capital (and shareholders' interests) is more important (and more valuable) than labor. The poor guy actually installing Ubuntu at Dell's factory is probably underpaid, even more than you or me are. He made some mistake, but that happens to all of us...
Errare humanum est, but the most interesting part comes next.