Hi,
I have a Dell Inspiron 1505 laptop running Linux Mint 20.3 Cinnamon version 5.2.7.

I'm trying to add a second monitor, a Dell S2421HSX, using an HDMI connection.

The monitor says it has no HDMI signal.
The laptop's Display dialog resolutely stays at Laptop default and Detect Displays button operates but does not change anything.

I tried using Driver Manager, but that reckoned everything was up to date.

HDMI connections seem firmly in place, and there are no alternative sockets to plug the cable into.

Disconnecting and reconnecting the HDMI cable at the laptop end causes the monitor to search again for a signal, so it seems the hardware connection is working.

I was expecting plug and play. Any ideas, please?

Inspiron 1505 isn't enough information. Install inxi if it's not already installed, then provide output from running it in a GUI terminal:Before you do, try inxi -U to try to get its built-in updater to bring it up to current from the old version in the Mint repos. Many distros block the -U switch. You can update or install from https://smxi.org/docs/inxi-installat...manual-install if so inclined.

If it balks at the y, try again without it. While you have the terminal open, try running:If my guess about the HDMI output name in use is correct, it might wake up that external display to a supported mode. If it rejects HDMI0, try again with HDMI-1 instead. If either is accepted, but not enough help, you can try repeating using --rate 60 or --rate 75 instead of --auto, with or without the addition of --mode 1920x1080.

It's possible you don't have enough VRAM to support both laptop display and 1920x1080 external, in which case --mode 1600x900 or --mode 1366x768 appended might be useful.

You have rebooted with the monitor plugged in? If not, do so.

Personally, I would give the thing no specs at all because X is very good at querying what's hanging out of the ports and doing what it can with what's there. If you end up with the same screen on both monitors we can fix that.

There is also a chance that the HDMI port is dead as that seems to be an old laptop.
I had the HDMI chip in my TV die, but other ports still worked.
Or maybe there is some crud in the port preventing good contact with the cable?

Thanks guys.
uteck: Possibility the port is dead, but the monitor did respond when I removed then reconnected the HDMI lead, so it must have seen something from the laptop's HDMI port.
business_kid: Yes, I did reboot with the monitor plugged in. Don't know what X is - I'm a newbie.
mrmazda: I did get some joy with inxi:

"
dale@dale-Inspiron-5415:~$ inxi -SGxx
System:
Host: dale-Inspiron-5415 Kernel: 5.4.0-124-generic x86_64 bits: 64
compiler: gcc v: 9.4.0 Desktop: Cinnamon 5.2.7 wm: muffin dm: LightDM
Distro: Linux Mint 20.3 Una base: Ubuntu 20.04 focal
Graphics:
Device-1: AMD vendor: Dell driver: N/A bus ID: 03:00.0 chip ID: 1002:164c
Display: x11 server: X.Org 1.20.13 driver: ati,fbdev
unloaded: modesetting,radeon,vesa resolution: 1920x1080~77Hz
OpenGL: renderer: llvmpipe (LLVM 12.0.0 256 bits) v: 4.5 Mesa 21.2.6
compat-v: 3.1 direct render: Yes
"

Also got:

"
dale@dale-Inspiron-5415:~$ xrandr --outputnHDMI0 --auto
xrandr: unrecognized option '--outputnHDMI0'
Try 'xrandr --help' for more information.
dale@dale-Inspiron-5415:~$ xrandr --output HDMI-1 --auto
xrandr: Failed to get size of gamma for output default
warning: output HDMI-1 not found; ignoring
dale@dale-Inspiron-5415:~$ cd /usr/local/bin && wget -0 inxi smxi.org/inxi && chmod +x inxi
wget: invalid option -- '0'
Usage: wget [OPTION]... [URL]...

Try `wget --help' for more options.
"

Does this help?

X is the Linux GUI similar to windows. The alternative is black screen with white writing and you have to type stuff instead of point & click.

run xrandr --properties and post the results

Please, when submitting command output, always enclose it in code tags to preserve the original formatting.

I asked for three inxi x's. Two don't supply all the information I'm looking for, though it does show that no graphics driver for your AMD GPU device was loaded by the kernel. The problem is that your 1002:164c GPU is newer than your kernel, thus not supported by Mint 20.3 as long as it's configured to use only standard repos.

--outputnHDMI0 was supposed to be --output HDMI0, so the entire command was invalid as submitted. The failed to get size message is a result of the missing support from the kernel.

Looks like you typed a zero where the capital letter O was required.

xrandr --properties won't add anything useful.

May be the leptop is not supporting monitor like that?
It is full HD one
Fn+F8 does work?
also try to enable some options in BIOS

Do you have another HDMI cable to test with? Or are you sure the cable works on other systems and monitors?