What Odin version are you using? Make sure you use the 3.09 (or newer if there is one), my phone sometimes doesn't get recognized on lower versions.
Also, what usb port are you using? If yiu have usb 3.0 and 2.0 make sure you try both and not just another port of the same type.
And last, make sure you have the most recent updates installed. One way is just Google it, another is plug in the phone when it's turned on and have windows dpwnload them automatically.