Try this:
ifconfig wlan0 down
iwconfig wlan0 mode monitor
ifconfig wlan0 up
airmon-ng start wlan0
airmon-ng check, and kill the processors that are interfering
If it don't work, try
ifconfig wlan0 down
macchanger -r wlan0
ifconfig wlan0 up
airmon-ng start wlan0
If this don't work too, fuck you and give us more info, bye mother fucker