The keyboard only fails when you try entering the password. Or stops working after you enter the password - is that correct?
Make and model keyboard?
Any error codes, messages, or pop-up windows when "typing" is prohibited?
Try the keyboard on another computer and try another keyboard on your Dell 8400 desktop.
Determine if the typing problem follows the keyboard or stays with the Dell.
Forum rules prohibit helping with password issues or password bypassing, etc..
Defective keyboards do not only affect passwords.