Reboot tapping F8 each second.
Select "Last known good configuration" at the menu
Or:
System Restore to Date/Time before issue started.
Reboot tapping F8 each second.
Select Safe Mode at the menu.
Start/All Programs/Accessories/System Tools/System Restore
Otherwise perform a Repair Installation: http://www3.telus.net/dandemar/repaxp.htm