Ubuntu doesn't detect my Bluetooth receiver, how to fix it?

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This is a Canonical question that will be signpost to solve Bluetooth issues. Please, whenever any of this answers does not fix your issue, provide the same information as this question in another question and add a link to this one. You should also provide what were the results/changes of each of the solutions.

For about two days now, my bluetooth has not been functional. The bluetooth icon is not present on the top panel. The bluetooth window is completely frozen as can be seen in this picture:

The output for bluetoothd -d -n is:

bluetoothd[3390]: Bluetooth daemon 4.98
bluetoothd[3390]: src/main.c:parse_config() parsing main.conf
bluetoothd[3390]: src/main.c:parse_config() discovto=0
bluetoothd[3390]: src/main.c:parse_config() pairto=0
bluetoothd[3390]: src/main.c:parse_config() pageto=8192
bluetoothd[3390]: src/main.c:parse_config() auto_to=60
bluetoothd[3390]: src/main.c:parse_config() name=%h-%d
bluetoothd[3390]: src/main.c:parse_config() class=0x000100
bluetoothd[3390]: src/main.c:parse_config() discov_interval=30
bluetoothd[3390]: src/main.c:parse_config() Key file does not have key 'DeviceID'

The output for start bluetooth is:

start: Rejected send message, 1 matched rules; type="method_call", sender=":1.343" (uid=1000 pid=19042 comm="start bluetooth ") interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)" requested_reply="0" destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init")

My Ubuntu version is 12.04. Any idea as to how this can be sorted?

EDIT

Patebin link containing the contents of /var/log/dmesg: link

EDIT #2

hcitool dev:

Devices:
    hci0    74:E5:43:36:65:21

cat /etc/dbus-1/system.d/bluetooth.conf: paste bin link

ps aux| grep bluetooth:

root      1065  0.0  0.0   4740  2028 ?        Ss   15:33   0:00 /usr/sbin/bluetoothd
dorsatum  2392  0.0  0.2 142772 10956 ?        Sl   15:33   0:00 bluetooth-applet
root     20960  0.0  0.2  76268 10780 ?        Sl   22:08   0:00 bluetooth-applet
dorsatum 21203  0.0  0.0   4388   832 pts/0    S+   22:13   0:00 grep --color=auto bluetooth

You may want to try loading the btusb module before starting the daemon:

sudo modprobe btusb

To make it happen on reboots put this into /etc/modules:

btusb

The above fixed my case, which was: sudo service bluetooth start did not start the daemon and dmesg showed

[   72.468338] init: bluetooth main process (4028) terminated with status 1
[   72.468401] init: bluetooth respawning too fast, stopped

because /usr/sbin/bluetoothd -n -d failed with

bluetoothd[4054]: opening L2CAP socket: Address family not supported by protocol

Use sudo service bluetooth restart

I had similar outputs and found an answer in this thread. Everything is back to normal for me now.