Ok. What exactly is not working with the network? Are you on wired or wireless? If you do run ip a, does your interfaces show up?

Another thing to look at is journalctl -b. Look for errors, lines in red, anything about the network. If you can roll back to a functioning boot (or run journalctl -b -1 should show the previous boot) and compare to that is probably a good idea, journald (displayed by that command) may contain errors that are not relevant, so comparing to a functioning boot may be good.

Also, depending on how old your computer it, there may be another hdmi output which uses the GPU integrated to your CPU. If that is the case, you could switch to it if the nvidia card stops working just to troubleshoot, take a look at journalctl -b and look for errors again. If the screen just goes black, and does not boot, this may also give you some messages as to why the nvidia graphics is not coming up.

To the menu to the left, there is one item called “secure boot”, and sometimes “fast boot” is there. However, if your computer is booting at all, I’m not sure this is it. But try it, it will not hurt.

GTX 580? Maybe you have to install an older driver, like the 470-series of the driver appears to support it: https://www.nvidia.com/en-us/drivers/unix/legacy-gpu/ Ubuntu has a bunch of older series of nvidia driver you can install for this purpose.

That would not explain your networking though. Unless that is also some older hardware too… But, a common thing to do as a new user in linux may be to find posts which answer “how do I install x in ubuntu” and they usually involve editing files under /etc/apt/sources.d/. This can wreck your system in this kind of way, so: have you done that? Or this is pure ubuntu, just regular apt update/upgrade and some apt installs?

Webb