RAS is truly a local area connection between two connections whereas, VPN is a local connection spread over large area.
You need to re-install another system, latest anti-virus software and an O.S with latest patches. Before you start your system, connect the infected HDD as a secondary drive then scan and clean the infected hard drive. Once done, you can copy the files into the system.
Default gateway is the IP address of the router in the network. In any case, if the users wants to switch on to another network, or if they cannot locate their particular network than their query will be forwarded to default gateway.