Comment 19 for bug 851345

At least for me it does not sound familiar to bug #864054 as everything from update to synaptic to external drives is working properly. Just the 3d-acceleartion did stop and therefore unity-2d is running. But the hardware is fully capable of 3d acceleration and a different kernel did not help at all.
The bug was once fixed by an update of lightdm as you can see above.