|A quick option to try is going back to Last Known Good Configuration|
To do that boot up your PC
As it is booting up tap the F8 key:
If that has worked you will see a black options screen
Use the arrow keys to select Last Known Good Configuration
and then press ENTER.
Hope it works.
By the way do you have a copy of the XP install CD? You haven't said anything about this. If you have then there may be other options available to you.
☺ When everything else fails, read the instructions.