According to your description such string appears in syslinux screen.

Verify if it was burned OK MD5SUM is 1ceb835d6b3c8e390d0ec4b6c913dc27. If is right, then such BIOS is really broken.

I've just checked. MD5SUM is OK.

Bios problem? It's been at least two years since I've installed arch linux (using AIF). I came from debian. My question is how/why my pc boots fine archlinux (x86_64 - grub2) all this time?

My pc has the same hardware. Nothing changed all these years.

A month ago after a problem (due to my mistake), locked me out of arch. I had to boot from a cd and to chroot to my system. I had switched to systemd already and it was a very tricky to use the old AIF cd I had.

That's why I've tried to get an updated installation cd for just in case but when I've tested it, I had this strange problem.

If it is possible please explain why this is hapening.

Feel free to ask me to do / test / check / anything you want.

> I've just checked. MD5SUM is OK.
Right :)

> Bios problem? It's been at least two years since I've installed arch linux (using AIF). I came from debian. My question is how/why my pc boots fine archlinux (x86_64 - grub2) all this time?
> My pc has the same hardware. Nothing changed all these years.
Since two years installation ISO uses syslinux as bootloader, previously grub (grub-gfx) was used.

> A month ago after a problem (due to my mistake), locked me out of arch. I had to boot from a cd and to chroot to my system. I had switched to systemd already and it was a very tricky to use the old AIF cd I had.
ISO version?

> That's why I've tried to get an updated installation cd for just in case but when I've tested it, I had this strange problem.
> If it is possible please explain why this is hapening.
If you hit "ESC" you will see a "boot:" prompt for syslinux.

> Feel free to ask me to do / test / check / anything you want.
You can try to prepare a syslinux boot usb-disk [#1]

[#1] https://projects.archlinux.org/archiso.git/tree/docs/README.transfer#n64

I've prepared a usb boot disk as described at the link above.

It boots but I've got the same problem as above. If a press nothing screen fills with L..............
If I press enter, the menu screen (archlinux istallation options) shows for a second and scrolls up filling the screen with m..............

I've pressed enter a lot of times to be able to read a message just before the scrolling up.

There are two lines. The first line says bla bla bla /vmlinuz .......
The second one says bla bla bla /archlinux.img ........ aborted

Then it scrolls up as the screen fills with m..............
Esc key at any point does nothing (ie I don't get a "boot:" prompt)

OK. Then syslinux does not work in your machine. You can try to contact upstream, maybe they can help to you to debug the issue and found a workaround.
You can also try other syslinux versions, compiling yourself or using precompiled binaries from webpage.
Anyway you can prepare a usb boot disk with grub, that works in your system, with arch/ directoy.

("aborted" if you did not hit any key?, weird...)

After some e-mails with syslinux guys we found that
the line "SERIAL 0 38400" in archiso_head.cfg causes me problems.
If I comment this line everything works as expected.

We managed to find the root of the problem.

I have a modem connected at my serial port (used as a fax machine). If the modem is on when I boot archiso cd then I have problems. If modem is switched off then everything works ok.

This happens because when archiso_head.cfg sets the serial port's speed (SERIAL 0 38400) modem responds back and this causes problems.

So if I want to install arch linux I must have my modem switched off. (or to delete line SERIAL 0 38400 in archiso_head.cfg)

Please mark this bug report as SOLVED with a workaround.

OMG!, thanks for debug the issue! A good thing to take care. :)