This command displays the contents of the Linux kernel message buffer. You may be asked to run it depending on your problems.
dmesg
dmesg
[ 2.817251] usb 1-1.4: new high-speed USB device number 5 using dwc_otg
[ 2.918993] usb 1-1.4: New USB device found, idVendor=7392, idProduct=7811
[ 2.919019] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 2.919030] usb 1-1.4: Product: 802.11n WLAN Adapter
[ 2.919041] usb 1-1.4: Manufacturer: Realtek
[ 2.919052] usb 1-1.4: SerialNumber: 00e04c000001
[ 194.192286] usb 1-1.4: new full-speed USB device number 4 using dwc_otg
[ 194.297324] usb 1-1.4: New USB device found, idVendor=0cf3, idProduct=3000
[ 194.297350] usb 1-1.4: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[ 194.303210] usb 1-1.4: Direct firmware load for ath3k-1.fw failed with error -2
[ 194.303265] Bluetooth: Firmware file "ath3k-1.fw" not found
[ 194.303307] ath3k: probe of 1-1.4:1.0 failed with error -2