windows xp login

Cannot log into window xp system to use computer, have
Dell dimension 4300 using windows xp, new 10/01. Since
system was first used I have been able to use system by
putting in user name and then hitting the Enter button
instead of entering a password. Last week after running
AOL checkup, computer gave a strange message so I tried
to reboot it to clear problem. When system came back up
it no longer allows access by using Enter key instead of
a password. Since I never used a password on this sytem
there is no password to enter. Only options on screen are
password or shutoff system. Unable to use computer. Have
tried rebooting, rebooting from safe mode, and called
Dell technical support, after an hour waiting for a
response the lady (in India) only offered reloading the
whole XP system and loosing all of the data on the
computer.
Does anyone have any experience with this kind of a
problem??