Hi,
I'm using a LG 34UC88-B monitor in a Arch Linux Installation and it's working fine.
My problem started when I tried connecting it to another computer, running Fedora.
I powered off the monitor, unpluged it, plugged it tto the other computer, powered the computer and then powered the monitor. In the first seconds everything seems fine, as I can see the booting screens with the computers brand and the grub screen. But then it goes black and the monitor complainss it is notr receiving any signal and that'll enter saving mode in 5 minutes.
I tried it twice, checked with another monitor and it works fine.
What might be causing this?

Thanks for all the help

Incompatible screen resolution being output from the "other computer" would be the most likely guess. Try forcing the "other computer" to use a lower resolution and see what happens.

Thank you for answering TEnTenths and sorry for the lateness of my reply.
When I try to coionnect to the "other computer", it defaults to a smaller resolution. I know this because the monitor "complains" about it. I never tried toi change the resolution to the correct one, because I thought I could do this after booting the OS.
So, it already is in smaller resolution, and it doesn't work in that situation.

Now days the display resolution is set in kernel user space instead of by the X server. When the display goes blank that is the point where the kernel switches modes.

There are many reasons kms isn't working correctly and could be due to the GPU driver. You could disable kms by using the nomodeset kernel parameter.

The arch wiki might help.
https://wiki.archlinux.org/index.php...l_mode_setting

Posting your distribution/version and GPU type might help.

Goes black while the Grub menu is on the screen, or after making a selection and the Fedora init process starts?

If the latter, try disabling Plymouth. At the Grub menu, with the highlight on the selection you wish to make, strike the E key, navigate down to the line (which may be wrapped) that begins with linu, then append plymouth.enable=0 before proceeding as the onscreen instruction indicates. Possibly it may help to also or instead to remove from that line splash=silent.

If neither of these work, try appending 3 to that line instead. Hopefully that will present a login prompt from which further diagnostics can be performed.

With some newer displays, trouble can sometimes be avoided by turning on the display before the PC.

While appending nomodeset likely will get you booted, you don't want to use it other than for diagnostic or repair purposes. Most likely you'll be presented with a low resolution mode that is seriously sluggish.