Earlier you had only two systems so point-to-point (one computer directly connected with the other) was working perfectly. Since you have now 3 systems, you will need one of the systems to have capability of supporting point-to-multi-point connection (one of your systems will act as server and both other systems will communicate through the server).
I am using this configuration at my home. Wireless network utility that comes by default in windows don't support point-to-multi-point connection. I have a MSI wireless card and their software support SOFT-AP (access point or act as server). Search on the internet about your wireless cards. If any one of your wireless cards support SOFT-AP or point to multi point connection then you can setup the network. Otherwise you will have to buy a wireless router and it will cost around at least 2,500 Rs.