Couldn't connect

So I tried to play on CDJ 850 the other day on PC mode and i couldn't it kept showing connection but never gave me the option to choose deck one or deck 2. The Mixer i was using was the Rane Twelve MKII and everything was loading up onto the laptop except when trying to use the CDJ 850 on PC mode I'm not getting through. I was using Serato DJ pro What do I need to do?