Folder Sharing

I am running WinXP Pro with SP2. Have recently gone to share a folder only to find that the whole 'Sharing' properties section is greyed out! I have shared other folders in the past with no problems. I've tried re-installing the 'file and print sharing' service, no luck. Also have looked over all the windows firewall settings, but can't find anything connected! I have not been able to find any related article on Microsoft's site. Please help! I need to share this folder!