Bluetooth adapter turned from working fine to unrecognized

Question

i had been using bluetooth fine, with devices working, but today when i turned on my computer again bluetooth strangely failed.

there is a bluetooth icon on the top bar, showing "bluetooth on", but if i click on the "bluetooth settings" item, a system settings window shows up and shows me a bluetooth on-off switch which is disabled (i.e. fixed to off).

more information about my case:

• i am a new linux used, coming from windows, and do not know supposedly-obvious commands.
• i am using a laptop. it initially doesn't have bluetooth. i bought a built-in type (instead of USB type) bluetooth module, and added it inside the laptop. hence, i do not have a specific FN+* key for bluetooth. in windows, i needed to install an additional driver that was intended for other machines in my laptop's seires which have built-in (i.e. factoryly built-in)j bluetooth modules. the Fn+* key seemed to only affect wifi under ubuntu.
• i have been successfully using magicmouse with my later-added built-in bluetooth module/adapter on both windows and ubuntu
• i have been trying to tweak the magicmouse scrolling speed with commands rmmod something, modprobe hid_magicmouse --scroll_speed=45 --scroll_acceleration=30 or something, then added a file `/etc/modprobe.d/magicmouse.conf". the mouse seemed to be working fine with these changes.
• now if i run commands like hcitool dev, the shell tells me that i do not have any "Devices" or "adapters".
• i seem to have bluez installed, because when i type "blue" then tab-autocomplete, a bunch of commands like bluez-test-device pops up.

-- update --

some commands and their results:

easoncxz@eason-Aspire-4741-ubuntu:/etc$ hcitool dev
Devices:
easoncxz@eason-Aspire-4741-ubuntu:/etc$ hcitool scan 
Device is not available: No such device
easoncxz@eason-Aspire-4741-ubuntu:/etc$ rfkill list 
0: phy0: Wireless LAN
    Soft blocked: no
    Hard blocked: no
1: acer-wireless: Wireless LAN
    Soft blocked: no
    Hard blocked: no
2: acer-bluetooth: Bluetooth
    Soft blocked: no
    Hard blocked: no
easoncxz@eason-Aspire-4741-ubuntu:/etc$ rfkill list 
0: phy0: Wireless LAN
    Soft blocked: yes
    Hard blocked: no
1: acer-wireless: Wireless LAN
    Soft blocked: yes
    Hard blocked: no
2: acer-bluetooth: Bluetooth
    Soft blocked: yes
    Hard blocked: no

Answer 1

Just figured this out and had the same symptoms as you. Make sure your Bluetooth is enabled in BIOS/UEFI. If it isn't it won't work :)