Try opening ports 1723 and 500 on your firewall with port forwarding to the IP of the NIC in your server that is configured for VPN.
Make sure your SMB2003 is set up for VPN whether it be PPTP or L2TP over IPSEC.
Make sure your fire is set to allow any incoming connections.
make sure you are using your public IP and not your private address of your server.
Are your AD users allowed for remote access in their user profile.
when you are at home are the 1723 and 500 ports on your router or firewall at home opened?