Because Facetime is a technology created by Apple, there is no official way to make a Facetime video call to a computer running anything other than Apple's OSX operating system. While emulators are available to run Facetime, it is not recommended as compatibility is poor.
By partitioning your PC's hard drive, you can install OSX Yosemite (Apple's latest operating system as of 2015) onto your PC allowing for use of Facetime, but as OSX Yosemite is coded for Apple devices exclusively, it is not recommended.
Emulators are available online, such as "iPadian," which allows PC users to run iOS apps and games on Windows, allowing for Facetime use.
Emulators and partitions are not recommended for install on a PC computer as Facetime and all of Apple's software are built for OSX machines and installing such programs on a PC could lead to potential "bricking" (compete failure of the device's motherboard) of the computer.
There are many Facetime alternatives for PC users, such as Skype, ooVoo, Google Hangouts and Jitsi. Skype, one of the most popular video and message communication platforms, offers free video calls, calls to land lines, messaging and more.
Google Hangouts, another Facetime alternative, offers up to 10-person video calls, group chat rooms and desktop to mobile calling, all free of charge.