"Error loading operating system"
 

This error is pre-lilo on a fresh install. The hardware is very old. I found it at an African public school running some ancient virus-encrusted XP install. I can boot it from my USB and use the operating system that way, but it has never successfully booted from its own HDD. It looks like this:

Updating ESCD... success
Verifying DMI Pool Data..........
Error loading operating system

And yes, the BIOS boot order is correct.

Now, during lilo install I get the following three warnings:

Warning: ignoring entry 'boot'
Warning: unable to determine video adapter in use in the present system
Warning: video adapter does not support UESA BIOS extensions needed for display of 256 colors. Boot loader will fall back to TEXT only operation.

The second two sound non-fatal, but the first sounds like it might be serious. The boot entry points it to /dev/sdb2, which is mounted on / (/sdb1 is swap and /sdb3 is /home).

As for the graphics, lspci returns a single graphics card:

01:00.0 VGA compatible controller: S3 Graphics Ltd. VT8375 [ProSavage8 KM266/K266] (prog-if 00 [UGA controller])

A kernel driver (something like SAVAGE??) is listed, but no modules. I don't really need help with the video adapter problem. Secondary objective, I guess.

SO. I'm not sure why the lilo isn't working. I'm considering installing to the MBR, but I don't really know what that is and I'm afraid of destroying my BIOS or something. The BIOS aren't on the MBR, are they? I'm going to go read some wikipedia articles. Please help?

bios not in mbr. read man lilo.
you must do *boot* flag on your /dev/sdb ( boot partition), and install lilo on mbr (
# LILO configuration file
# generated by 'liloconfig'
#
# Start LILO global section
# Append any additional kernel parameters:
append=" vt.default_utf8=0"
boot = /dev/sda2

AS WiseDraco points out did you when you partitioned your drive select the the boot drive with the boot flag.
this makes a small spot on the first sector for lilo to live on.
it is a typo when you put it in. you either typed in the kernel wrong. location of the kernel.
lilo only Warning: ignoring entry 'boot' when it is unable to find that kernel.

make sure your /etc/fstab entry reflects the location of /
that is where the system is.
root=/sdXX ro vga=normal
and /etc/fstab should be /dev/sdXX / ext(yourchoice) defaults 1 1

did you place lilo on the MBR ?
trying to find the boot sector and load lilo
Then lilo will try to map the info of the motherboard find /boot/vmlinuz.This means no lilo on boot sector.
reinstall lilo so it points to the kernel and is in sync with your /etc/fstab

id say, there is no lilo loader - fstab and kernel come far later.
if system is installed from dvd and at end of installation choosen "simple lilo" installing methode, then that's look strange.
try to boot from the same install dvd and do kernel options -
huge.s root=/dev/sda2 rdinit= ro

then you must boot in your installed system, and can run midnight commander ( mc ), edit /etc/lilo.conf and update lilo boot record ( lilo -v -v ). also check for boot flag - do
cfdisk /dev/sda

I agree

You are right Wisedraco but I always try to explain the complete lilo boot all the way through encase he did a chroot install from the usb.

The practical thing for the OP to try next is to re-install, choosing only the huge kernel, and install lilo to the MBR in the "simple" way (simple -- Try to install LILO automatically) during the installation process. Of course a re-install is unnecessary but that's most easy to do for the OP, I think.

BTW, LILO does not check for active partition. LILO does not know about "partition" at all. Correct me if I'm wrong.

Your correct, lilo uses sector maps to load but can also function as a basic DOS MBR loader and switch to another partition but only if it was configured to do so when installed to the MBR.

FYI The boot flag on the partition is used by the DOS boot loader, not by any Linux boot loader ever written.

If lilo is installed to a partition then the partition must be the only one with the bootable flag set and a valid DOS MBR must have been installed on the disk.

Since DOS is more or less dead these days you should always install lilo to the MBR else various BIOS error messages will be seen as the BIOS can not find any code in the MBR to use.

EDIT

To clarify the following message is a BIOS message and it means there is no code in the MBR to load :-

Error loading operating system

This is not a result of lilo pointing to the wrong root partition or an invalid kernel image, if lilo was getting loaded but had an invalid configuration then you would see "LI" at the very minimum in the top left of the screen.

I've been in the trap of not setting the boot partition active when using syslinux. That took me quite a few hours to sort out. Maybe everyone else knows that but just in case ...