Connect Securely With a Software VPN
Remote Access and VNC are convenient but insecure protocols; a data thief can easily intercept and read unprotected transmissions. If you connect to a remote PC within a secure, local network, you're unlikely to be compromised. But you need to take precautions when connecting over the Internet.
A VPN creates an encrypted path for your data. This renders your information difficult to intercept; and if it is captured, a thief will have great difficulty unscrambling the content. Some high-end routers include VPN hosts. If yours does, consult your documentation for instructions on how to proceed. (Actually including a VPN host is different from merely allowing VPN pass-through connections, a much more common router feature.) You could even hack a router to add this capability.
Setting up a software VPN is simpler, though you have to install it on each remote PC that you may need to reach. I like LogMeIn Hamachi, which is free for noncommercial use. Here's how to configure that tool.
Install and launch Hamachi on both PCs, and then enter a nickname for each. On the host PC, click the triangle icon at the bottom of the window, and select Create a new network. Enter a network name and a strong password, and click Create.
On the client PC, click the triangle icon, and choose Join an existing network. Then enter the network name and password, and click Join. You can now securely interact with the other PC as if it were on a local network. Connect by identifying the computer name, or type the Hamachi IP address (instead of the internal IP address).
Connect With a Free VNC Server and Client
VNC is a traditionally open client-and-server protocol for remote PC control. Many VNC setups are interoperable and span different operating systems; even smartphones can control a VNC-enabled PC. Some host software includes more-advanced features (such as encryption) that work only with its clients, but in most instances you'll be able to connect across brands in basic modes.
The VNC process is great if your version of Windows doesn't include Remote Desktop. Instead of activating operating-system tools, you just install host software on the PC that may need to be reached and client software on the computer that will take control. Here's how to get started with RealVNC.
Download the free version of RealVNC. This app will power basic connections, with a few important caveats. I'm comfortable using it on a secure home network, but I don't use it online unless I'm tunneling through an encrypted connection, such as with LogMeIn Hamachi. Otherwise, the free edition adheres to the basic, insecure VNC standard. Consider upgrading to a paid version for improved security and many other features.
Run the RealVNC installer on the host PC. In the middle of the process, you'll encounter a setup screen prompt. Click Configure to enter a password, and then finish the installation. On the client PC, run the RealVNC installer again. If you want to view only the remote system, check the box for VNC Viewer only. Open the client application (Run VNC Viewer), enter the server's IP address, and click OK. Enter the password, click OK, and you'll have a connection to the remote PC.
Connect With a Proprietary Service
VNC and Remote Access might be able to satisfy your need to control a remote PC, but they can be complicated, and without additional software, they offer minimal security. In addition, many home routers have difficulty passing the connections to their private network. To offset these limitations, you might want to consider one of several proprietary services.
LogMeIn and GoToMyPC, each available in free and paid versions, can simplify the entire process. You install a server application on the host machine, leave that computer online, and then connect through a Web browser anywhere else. Best of all, since you're connecting through the Web site, you can reach a home PC with a dynamic IP address, and your router should support the connection. LogMeIn even works from an iPhone.