It sounds like you're running into some trouble with the Font Awesome 4.3 widget library–is this right? In order for their icons to be displayed, the Font Awesome widget libraries do require that their corresponding Font Awesome fonts are installed locally on your computer. This guide for setting up and using the Font Awesome widget libraries in Axure RP and on Axure Share should help you with getting started with this:
I also wanted to mention that if you're currently using Axure RP 8, all of the icons in the default "Icons" library do consist entirely of Font Awesome icons, so you also have the option of using those as well.
Hopefully this helps! Please let me know if you have any questions or if you're still running into any trouble with this.