Lighting not building in UE4

Hey everyone,
I am having some problems with getting my lighting to build. I have searched and searched the internet for a solution for this and I cant seem to fix it. I have my lightmass incoming connection going through my firewall but still it doesn’t work. I even tried downgrading my xcode to 8.2.1 thinking that may be the cause. Unfortunately, it didn’t work. At this point, I don’t know what to do. I am a beginner at UE4 so I am still learning. I am hoping it isn’t a hardware issue. I need to find the solution to my problem asap because I need this for school. Any help is very appreciated! Thanks!