I did a quick search of the c000021a error message and got the feeling 
that it's referring to a Windows booting error. There were many fixes 
listed. I am not sure which one I would follow. Since you said you can't 
get to the Boot menu, can you get to the BIOS or setup of the laptop? I 
when to Dell and I think the setup is accessed by pressing the F2 key 
while starting the computer. If you can get into BIOS or setup you can 
usually choose how to boot the computer. You can usually check the 
keyboards by using them to navigate around the setup menu too. From 
working on laptops/desktops I have found that CD drives fail and so do 
keyboards. So you could be working with a bad CD unit or Keyboard.

On 10/6/2010 9:23 AM, Hachmeyer, Mr. Paul S. wrote:
> A friend brought me his Dell Latitude D610 laptop which gets this error when booting.  I can't get into safe mode or any other option, whichever I select, once it starts xp, it craps out.  If I try to select another boot device, I can't get to the cd drive selection, seems like his 'down' key is broken, and the 'up' key doesn't wrap to the bottom of the boot selection list.  Options on the web suggest reinstalling or repairing xp, but I can't get the cd drive selected.
> I'm not sure what sp is installed, can't get in to check that.  Seems to have been a few os program glitches over the years with xp that might cause this message.  There is no Norton or Symantec software installed (backup apparently was another problem causing this message), and the memory chip was popped out and replaced, since sometimes that causes the error.
> Any ideas?
> ....

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