Network/Workgroup/Password Issues

This morning 2 of the network PC's will not connect to the server. Somehow the workgroup on both had changed. Have fixed this and can see all PC's and the server. When I try to connect I get asked for a password and user name have never used either. Have gone in to Local Polices?security options and disabled the user passwords prompt on both PC's and the server. Still asks for a password and user name. The PC's with issues are both Win & pro. The server is Server 2003. Stumped on how to fix this.