Can't boot, black screen, "Safe mode" stuck at agp440.sys driver

In order to increase exposure, I decided to repost previously asked question
again, adding little more details.
I have following problem:
Due to fact than my webcam software conflicts with on of my video programs,
every 1-6 weeks I am forced to reinstall both, in order for both of them to
work (did it numerous times in past for period over 3 years - never observed
any problems). Every time when I reinstall any program, my: AdAware, Window
Defender as well Kerio firewall produces large number of pop-ups (usually
referring to registry changes, application starting other application – etc)
– which I typically click “allow” without reading all detail, knowing that
such behavior during installation is normal and expected.
Last time during webcam reinstallation while clicking pop-ups I registered
that Adaware produced pop-up referring to something called “%Root%” – (part
of string, most likely some registry change) – which I clicked “allow”.
When I rebooted PC (part of webcam installation process), Windows screen get
to “Windows” logo (part of booting process), than hang on black (lightly
highlighted) screen, never reaching “Welcome/log in” screen. Rebooting it
again prompted me automatically to “choose safe mode” screen. No matter what
safe mode option I choose, when booting in safe mode, screen always stuck at
“agp440/sys” driver (booting in safe mode displays long list of drivers
loading – usually reaching “agp440” – than it stuck).

I did lot of online research and already tried number of approaches – here’s
what I tried already:

1. Tried using: “boot using last good configuration”
2. Tried instruction from following article:
http://support.microsoft.com/kb/324764
Article above describes problem caused by agp440 driver (symptoms match),
advising disabling it from boot list. Following instruction I disabled it
which caused Windows to stuck on “mup.sys” driver (in safe mode) instead.
Mup.sys displays immediately before agp440 on safe mode “load drivers”
screen. After unsuccessful trial I enabled apg440 back to original
3. Tried following commands from Windows Recovery Console: SCANDISK, CHKDSK,
CHKDSK /p, CHCKDSK /r, - last one produced result “one ore more problem has
been found and corrected by Windows”
4. Tried “FIXBOOT” command from Recovery Console (not sure of wisdom (or its
lack) of this step)
5. Tried coping “agp440” from working not affected copy of Windows (which I
have on another Hardrive) and replacing agp440 with copied one on not booting
Windows – using recovery console command prompts.
6. Following advises found online I tried changing some options in NETBIOS
sector (some I couldn’t find while other didn’t produce any results) – all
restored back to original state (before any changes).
7. Following some online suggestions, I tried disconnecting all USB
connected devices before and after booting (webcam, external HDD, keyboard,
optical mouse, power cord)
8. Following advices I tried swapping (and removing one) memory chips.
9. I scanned affected hardrive with “Spin Rite” recovery software from GRC
(designed to locate and check HDD for errors) – results came “no errors or
bad sectors”.

Affected PC is Dell Laptop (Inspiron 8600) with Windows XP SP2 Professional
version 2002 - fully patched, legal copy, Pentium 2GHz, 512 RAM, NVidia
GeForce FX Go5200 video card.

Fact that different HDD works on same PC without any problems, seems to
suggest troubles are not hardware related. Not booting HDD contains some very
important to me personal data files which I would like to recover. According
to some found online advices, deleting entire C:\Windows from Recovery
Console, and installing fresh copy of Windows over it, would not affected my
private files and folders. I was scared to try this option without conforming
first that indeed my personal files would survive. While posting here I was
referred to MS article which claimed files “might” be lost. Also some people
suggested that I could use DOS CD, boot from it and use DOS to recover files
from HDD. Wondering what community thinks about suggestions.

Internet floods with post relating to this issue, suggesting that huge
number of people experiencing same problem (all post seems to have common
factor: NVidia video card, even particular reasons and solutions to problem
seems to vary). From found online discussions, most suggest that problem is
video related, speculating that Windows is trying to load screen settings
which it cannot understand – hence it stuck. Fact that my problem occurred
while installing “video related” software seems to confirm this. Some other
people has been speculating that it might be not agp440 driver which produces
problem at all, but one immediately after it (assuming that safe mode display
shows apg440 loading and that’s next driver which doesn’t load). Posts were
referring to some ASCI driver as next one (???) – couldn’t find any ASCI
driver (which suppose to be listed on NET BIOS according to post).

Even this probably has no any significance to problem, just would like to
mention I was forced to reset “Administrator” account password in order to
get to Recovery console. I don’t remember have I disabled “Administrator”
account totally (some info on screen while using reset CD seems to suggest
this), or just forgot its password. In any case I tried log in with password
of “User” (with administrative privileges) account which I created and have
been using to log in - which to my knowledge should use same as
“Administrator” account password (unless I screwed something while
configuring Windows after installation) – and it didn’t worked. I made boot
CD and used instruction for this purpose from site below than successfully
reset password to “blank”:
http://home.eunet.no/pnordahl/ntpasswd/

Wondering does anyone have any suggestion I could try and what community
thinks about reinstalling new copy of Windows over old or trying DOS? Would
there be any safe way which would prevent loosing files while doing this?
Perhaps some personal experience when files were not affected versus when
they were?

[rmkmonk]

Without doubt this is a hardware problem, and you know what, it's that most forgotten piece of hardware - the memory! I had excatly this problem, and only after I NOTICED THAT THE bios WAS POSTING AN INCORRECT memory size did I remove two 512mb chips (I already had 2 other 1 gb chips) and hey presto, not only did everything work, but is has never run so fast!

I think what must be happening is that AGP440.sys must be loaded into a part of the memory which has failed, so there it hangs.

Another point, my sister had a Dell with the same problem, and it was down to the extremely cheap (sorry Dell, but it is true) memory chips Dell uses in their home computers!