Android : ADB doesn't recognise device anymore

A whole line of tablets don't show at ADB devices anymore (they worked just fine one week ago). Other Android devices do work (like my Nexus 5 phone). This is first time I face this problem. I've read and tried most solutions I've found at SO and other sites to no avail. Here's the situation:

• They show in lsusb as Bus 010 Device 004: ID 18d1:dddd Google Inc..


• Created/edited /etc/udev/rules.d/51-android.rules and added SUBSYSTEM=="usb", ATTRS{idVendor}=="18d1", MODE="0666" (and several other attribute combinations here).


• Restarted udev via sudo service udev restart.


• Restarted ADB server via adb kill-server; adb start-server`.


• Tried all USB ports on PC.


• Tried another USB cable.


• Restarted PC and tablet.

A strange thing is that even if I empty /etc/udev/rules.d/51-android.rules file and restart the udev daemon, adb still detects my Nexus 5 phone.

Changes I remember I did before this problem started to happen:

• Started using Android Studio instead of Eclipse (although I'm using the same ADK) and tools)


• Upgraded Ubuntu to latest version 14.04 (maybe some udev changes/problem here?)

Any further suggestions are welcome, thanks in advance.