Good point ethics. I just updated Samba on FC5, and for some reason, the requisite service were turned off in chkconfig.
neddis - if ethics is correct and it's the stopping part of restart that doesn't work, try
chkconfig --list | grep smb
to see if the service is set to start automatically
Also, the firewall can stop you accessing anything, but it won't cause Samba to fail per se.