Failed to connect MIDI DDJSR

I have a Pioneer DDJ-SR. Every time I try to connect it to Serato DJ Pro it says MIDI failed to connect. I have tried it on THREE different computers and they all say the same thing. I got a new USB cable, redownloaded Serato DJ PRO and installed the drivers and they keep saying the same thing. I tried on two windows computer and one Mac book. Anyone know why this is happening?