So there are technically 3 IP address types.
There is localhost (your own computer) (also called a loopback address)
There is your internal address... usually 192.168.X.X
There is your external address which your friends are using to connect I presume.
The address you need to use is the internal address of the desktop from your laptop to connect to the server.
To get that address, on the desktop, run command prompt and type ipconfig. You want the IPv4 address. Try connecting using that on your laptop.