once I had a problem like this, and I solved it by adding the following
section to xorg.conf:

Section "ServerFlags"
   Option "AllowEmptyInput"    "false"
EndSection

it happened earlier this year when I upgraded x11-base/xorg-x11.

-- 
Crístian Deives dos Santos Viana [aka CD1]
Sent from Campinas, SP, Brazil