Don't be shy about getting up a bit closer and being closer can reduce room noise and depending on the mic can yield a more 'radio' like voice (bassy) due to proximity effect. With the distance I suggested and a normal speaking voice I would guess the gain knob might be about 12 to 2 o'clock to get the UM2's green signal LED to flicker on peaks of your voice depending on distance. The mic has a sensitivity spec of 15mv/PA which is about middle of the road for condenser mics and should give an OK signal into your interface. Sitting close is how close? For speaking you may want to be around 8'(20cm) to 12'(30cm) and be talking directly into the grill on the side of the mic with the MXL logo. Audacity can not use ASIO, but the interface will show up in the options for input and output device if the interface is connecting OK. You could also try to record this hum to check the USB connection to the computer and the software. This will check to see if audio is getting into the interface. While touching your finger to the tip of the plug on the loose end of the cable, turn the gain up on the plugged in channel and watch to see if the SIG Led turns green to indicate a signal and listen in the headphones for hum. If by chance you have a 1/4'(6.5mm) instrument or patch cable, plug it into either the #1 Line input in the combo jack or the #2 INST input.

It may or may not be the cause of the mic not working, but something easy to try. Since you're using Win10, check the setting for 'Windows 10 camera, microphone, and privacy'. Click to expand.- Are you hearing audio played from FL Studio or Audacity through the UM2 in the headphones or were you just stating you know the headphones work?

Behringer umc404hd windows 10 driver