You can try https://www.plop.at/en/bootmanager/index.html

Do you have installed grub on mbr?

when you boot from C, does it seem that it's looking for a floppy to from after unsuccessfully booting from the hdd? if so, could be buggy virus residing in the MBR. you can try using my antivirus tool after booting from the floppy, run VCHECK C:
if it detected something don't forget to take a screenshot .

good luck

I think DOS FDISK /MBR command started from floppy is better than trying some unknown antivirus...

ahuska wrote on Yesterday, 11:43:

You can try https://www.plop.at/en/bootmanager/index.html

Plop won't make any difference here. It's just a boot loader.
The problem is not the boot loader I use on the hard disk, the problem is the computer can't find any bootloader on a disk.

ahuska wrote on Yesterday, 11:45:

Do you have installed grub on mbr?

Yes.
In fact I use Lilo, not grub, because I have an old Ubuntu Hoary on a partition, for old Linux Loki games, and it's fun with a Voodoo2.
Hoary came with Lilo, not Grub yet.
The goal of the floppy is to boot the bootloader on the disk mbr. Which works. Because the Pc can't find it by itself ...
lilo.conf :

lba32
boot = /dev/fd0
install = boot.b
map = map
compact
prompt
timeout = 2
read-only

other = /dev/hda
label = hda

Masaw wrote on Yesterday, 12:09:

could be buggy virus residing in the MBR. you can try using my antivirus tool after booting from the floppy, run VCHECK C:

If I plug the hard disk on another computer, it works without any problem.
And this doesn't explain why it also refuse to boot from USB or LAN.

I think there's a weird physical problem.
I got this computer for free, it was on the sidewalk waiting for trash.
There's an internal USB connector for the front panel, and the place where there's a fuse has literally burned, and there was a short 😀
I have fixed this, and the computer used to work normally for a while. Then it stopped finding any boot other than floppy ...
Too bad, it's a nice machine for Win98. Even if the Intel video card is a bit weird, and other PCI problems with an Aurel Vortex, 3DMark99 gives 6000 pts, and Unreal get 45 fps average in 1024x768.

The boot= parameter in lilo.conf is where you want to install lilo. And you install it on floppy.
imho you have bad ( or incompatible with this mb ) mbr on hda.
What OS is ( or you want to install ) on hdd?

And with plop you can boot from usb.
You can try it instead of microsoft's mbr - but use backup.
https://www.plop.at/en/bootmanager/mbrinstall.html

Well, I know how to install lilo or grub on a hard disk.
And it's installed now, since I can boot this disk on another computer.
The problem is the mainboard which can't find any mbr on a disk or even accept to boot from Lan or Usb. as it's supposed to do.

This lilo.conf is the one installed on the floppy.
Then it redirect on /dev/hda, where there's grub. And not lilo as I wrote before, but this makes no difference here.

You should try start same bootloader from floppy and from hdd so you know if on your system is problem with bootloader or with hdd booting.

nali wrote on Yesterday, 06:00:

In the bios, "Boot Sequence" there's only "ǘ⧫" and Floppy, where I would expect to see Lan and Usb too.

any chance you could post a photo of this, just to stop the comments about the bootloader or mbr being the problem ?

nali wrote on Yesterday, 15:38:

... If I plug the hard disk on another computer, it works without any problem. ... and the computer used to work normally for a […]
Show full quote

...
If I plug the hard disk on another computer, it works without any problem.
...
and the computer used to work normally for a while. Then it stopped finding any boot other than floppy ...
...

nali wrote on Yesterday, 06:00:

I reflashed the bios, reset to default, no change.
In fact, even if I hit F12 to enter the Boot choice, I get the message "No boot device available", excepted if I choose floppy.

I wish I could give an answer that would resolve it.
I'm thinking memory problem or eeprom problem.

I know people try to help, but many don't really read before answering 😀
Not a new thing.

An eeprom could be a possibility.
I got this computer for free on the sidewalk.
There was traces of burn near the internal connector for the USB front panel. I had to clean it and replace the fuse.
The Dos tool Delldiag still says "overcurrent on USB B".
But the PC worked for a long time after I fixed it.

nali wrote on Yesterday, 19:50:

I know people try to help, but many don't really read before answering :) Not a new thing. https://i39.servimg.com/u/f39/12/47/4 […]
Show full quote

I know people try to help, but many don't really read before answering 😀
Not a new thing.

An eeprom could be a possibility.
I got this computer for free on the sidewalk.
There was traces of burn near the internal connector for the USB front panel. I had to clean it and replace the fuse.
The Dos tool Delldiag still says "overcurrent on USB B".
But the PC worked for a long time after I fixed it.

The photo clarifies things, and I have a vague recollection of something similar on a computer but can't remember it.

and since you mentioned already having reflashed the bios and defaults....

I'd try that again without any unnecessary devices/cards attached to the mainboard, no idea if your dell has bios defaults and optimized defaults or custom defaults options, but I'd try them all and check the boot selection afterwards for any change. even changing the boot order in the bios and saving it. if possible even try to revert back to an older bios version, though I see that on the retroweb there is only one biosfile available.

The USB overcurrent thing clearly indicates that there likely still is a short on the front? USB port. but that's another problem. could be broken sensor. Do you have the correct voltage, ie 5V there?