The issue that your having with booting could be simply something like the RAM needing to be reseated or replaced to the operating system needing to be reinstalled. Elements of your OS can get corrupted over time. A fresh install would do a lot. You could reinstall the OS to its factory state and see if that resolves it.

CTRL + F11 I think brings you into the recovery console on a Dell at boot. You can restore it to its factory state from there.

You can get loads of tools that will allow you to delete or recover the password on xp. What you can also do is turn on the administrative account through dos, boot into that and remove the password from the other account.