Kernal stack inpage error

A friends Sony laptop a few years old on XP, is not logging on, giving a blue screen of:

<i>Kernel stack Inpage Error -
which is preventing windows from opening. These are the instructions its
giving me:
-Check to make sure any new hardware or software is properly installed.
If problems continue, disable or remove any newly installed hardware or
software.
-Disable BIOS memory options such as caching or shadowing.
-If you need to use safe mode to remove or disable components, restart your
computer, press F8 to select Advanced Startup Options and then select safe
mode.
</i>

He doesn't really know how to go about this, and I'm not totally sure of the problem and how best to solve it. Can someone please advise what has happened, what he's best to do (whether an above option or not) and describe point by point how to do it. He needs the laptop back ASAP to do important work. Many thanks.

Can you get into Safe Mode?

Also the exact error code would be helpfull. Something like: 0x00000077

The master boot record might be infected with a virus.
Start scanning with your Antivirus. + run on line virus scans, from this links:

http://www.bitdefender.com/scan/licence.php

http://housecall.trendmicro.com/

http://www.windowsecurity.com/trojanscan/

+ download Spybot.
http://www.safer-networking.org/en/index.html

It also could be a faulty RAM memory stick.
Download Memory Test, and run it for a couple of hours.
http://www.memtest86.com/

Disable "System caching" in BIOS to see if this resolves the error.

Enter BIOS setup, by pressing the "Delete" key at bootup (or other key if indicated). Use the arrow keys to scroll.
When you have disabled "System caching". Save the settings in BIOS, before you exit.

Also run windows chkdsk.
start > run > cmd
in the new window type chkdsk/f
when prompted to run on boot choose Y & reboot
this will check for & fix any disk errors.

If you cannot enter Safe Mode then you will need either your XP CD & or OEM recovery disk to enter the Recovery Console as a next step.