Comment 6 for bug 1330255

I think I have find the problem

New DELL keyboards haven't Numlock key but BIOS config has "Numlock active" on "Yes". I've have changed it to "No" and problem vanishes.

I suppose the system tries to change Numlock state and, if no movement is detected on keyboard or mouse all two became hanged.

When the keyboard isn't a new DELL one, for some reason I don't know, sometimes doesn't work.

I've changed all new Dell to "Numlock Active" to "No"