Managing Network with Windows 2003 Server

I am managing a small network with Windows 2003 server that is being set up with Domain Controller, DHCP, DNS and File Server Roles. I also used RDP for server maintenance and it works perfectly fine with no errors. However, when I try to access the network using VPN connection with a remote user, everything has stop working. The LAN users could not be able to have an IP address from DHCP Server. I tried to set the computer using static IP but it still could not access the PDC. I am receiving a time out or unreachable message when trying to ping the server to test the connectivity and removing RRAS is not working either. Can anyone help me resolve the issue?
