No APM connect

I get flashing lights when I connect my apm 2.5 to the computer. But I am not getting any com port connection. What to do? I think I need to reflash the firmware? Thru another port? Thanks!

@BillAPMPilot,
What ArduPilot firmware and what Ground Control Station are you using?
Is your APM2.5 a genuine 3DR product?
Regards,
TCIII GM