Check the registry entries. You will be very unappy with Domain communications if, as in this case, your cannot start your Winlogon and Server Services from the workstation.
If this is exactly your problem, the most common cause is either your have msblast or a newer variant, or you removed msblast with a removal tool that left these services unstarted as an unintended side-effect.
1. Try restoring the original registry entries for all service entries. It does depend on your version of XP. BlackViper's site has some .reg files you can use:
2. If, after a reboot, your services are still not starting, do a maintenance reinstallation of the OS. There are things possible by accessing the OS that cannot be done simply with registry changes.
3. If that is not working, do a clean install.
Make sure you are absolutely certain that in your case the issue is identical to the one that started this thread: Winlogon and Server services cannot start. I would really hate to see you have other likely issues that show similar symptoms but not identical solutions.
You can always check your services through Control Panel, Administrative Tools, Service. You can always do a Start, Run services.msc.
If you really cannot re-start the services, a repair installation or unfortunately a clean install is often the shortest answer.