It’s not clear if you are asking about:

Windows XP Welcome screen login password, required after boot process has loaded Windows XP

Or

System password, required before allowing boot process to load Windows XP

To clear unknown System password use the 2-pin password jumper on the system board

For Dimension 2400 click here & follow instructions

I think it's the XP Welcome Screen password. If I had the PW, and entered it, I'd be all the way up and ready to use the system. Do you know how to resolve this prblem? (She bought the system new from Dell, and I've heard that they might supply an OS Disk if asked?)

Is it XP Home Edition or Professional version?

if you lost the password for the only user account listed on the welcome screen then there is probably a simple way to reset it.
to do this you need to start the computer in what is called 'safe mode'.
to enter 'safe mode', power on the computer and begin striking the f8 key (f8, f8, f8, f8).  you should do this when you see the big dell logo screen.  if the windows banner screen appears then you were too late and will have to shut down the system and then start it back up and try again.  if you do it before the windows banner screen appears you will be presented with a a list of start up options one of which is called 'safe mode' (not 'safe mode with networking' or 'safe mode command prompt').  next you should see the wecome screen that has not only your familar user account name (with unknown password) but also an account called 'administrator'.  click the administrator account and you should automatically be logged in (if prompted to enter a password just hit enter - there is no password unless someone, you, changed it).  once windows is loaded it won't look completely normal but should still look familar.  click start-run-and type in "control userpasswords2" (without the quotation marks) and click ok.  then click on your user account name to select it and then click the 'change password' button.  finally, shut down and try to restart normally and log on as your old self with the new password.  let us know how it works out.

Hi - sorry it took so long to get back to you, but I had to go out of town last week.

I tried what you suggested - but never got an 'Administrator' option.  I booted 'Safe Mode' and it only gave me my duaghter's ID - which is where it asks for a Password.

Any idea what I can try next? 

She didn't receive a bootable disk with the system, and never created one.  She took this system to her college dorm - and her primary use was to chat and write papers.  She knew nothing about backups or maintenence.  Then she put it away when she got a laptop and forgot all the passwords and stuff.  Now she wants to use it again. 

Can I get a boot disk from Dell or Microsoft?  (I don't have a Key for Windows - she never had to install, and didn't keep good track of things.)

And if I get a boot disk, can it be installed without using Administrator? 

On Vista, there's an option to restore to factory install, but I can't find this option under XP (Home Edition).

Any advice is appreciated.  

I have successfully used a freeware product called ophcrack before.

Basically,, the software has you create a boot disk, which you then boot the computer to.

It will search for windows passwords like the missing oone and tell you what they are....

Thanks very much. I'll try the ophcrack approach next week.  I have found the backup OS disks she lost, but haven't gone through them to see what I have.  But a death in the family has me going out of town for a few days before I can work on this again.