Start in Safe Mode and put your login name back.
From XP HELP
[To start the computer in safe mode
You should print these instructions before continuing. They will not be available after
you shut your computer down in step 2.
Click Start, click Shut Down, and then, in the drop-down list, click Shut down.
In the Shut Down Windows dialog box, click Restart, and then click OK.
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When you see the message Please select the operating system to start, press F8.
Use the arrow keys to highlight the appropriate safe mode option, and then press ENTER.
If you have a dual-boot or multiple-boot system, choose the installation that you need to
access using the arrow keys, and then press ENTER.
Notes
In safe mode, you have access to only basic files and drivers (mouse, monitor, keyboard,
mass storage, base video, default system services, and no network connections). You can
choose the Safe Mode with Networking option, which loads all of the above files and
drivers and the essential services and drivers to start networking, or you can choose the
Safe Mode with Command Prompt option, which is exactly the same as safe mode except that a
command prompt is started instead of the graphical user interface. You can also choose
Last Known Good Configuration, which starts your computer using the registry information
that was saved at the last shutdown.
Safe mode helps you diagnose problems. If a symptom does not reappear when you start in
safe mode, you can eliminate the default settings and minimum device drivers as possible
causes. If a newly added device or a changed driver is causing problems, you can use safe
mode to remove the device or reverse the change.
There are circumstances where safe mode will not be able to help you, such as when Windows
system files that are required to start the system are corrupted or damaged. In this case,
the Recovery Console may help you.
NUM LOCK must be off before the arrow keys on the numeric keypad will function.]
