Hi,
You could try the following.
Shut down the notebook. Tap away at f8 as you start the notebook to enter Windows Recovery Console. Use the arrow keys to select Safe Mode and hit enter. If windows will load in this mode, from the Start Menu, click All Programs, click Accessories, click System Tools and launch System Restore. Pick a restore point at least 24 hours before the log-on issue and then proceed with the restore process. When complete, Windows will reboot as normal so check if you can now log in correctly.
Another option if the above does not help is as follows.
Shut down the notebook. Tap away at f8 as you start the notebook to enter Windows Recovery Console. Use the arrow keys to select 'Start Using Last Known Good Configuration' and hit enter.
Regards,
DP-K