Booted up and X dies.
Messages in /var/log/Xorg.0.log.old include
46:[ 20.239] (EE) systemd-logind: failed to get session: PID 954 does not belong to any known session 75:[ 20.251] (EE) Failed to load module "nv" (module does not exist, 0) 114:[ 20.255] (EE) [drm] KMS not enabled 115:[ 20.255] (EE) [drm] KMS not enabled 116:[ 20.255] (EE) [drm] KMS not enabled 117:[ 20.255] (EE) [drm] KMS not enabled 118:[ 20.255] (EE) [drm] KMS not enabled 126:[ 20.256] (EE) open /dev/fb0: No such file or directory 134:[ 20.256] (EE) open /dev/fb0: No such file or directory 137:[ 20.257] (EE) Screen 0 deleted because of no matching config section. 139:[ 20.257] (EE) Screen 0 deleted because of no matching config section. 142:[ 20.257] (EE) Screen 0 deleted because of no matching config section. 144:[ 20.257] (EE) Device(s) detected, but none match those in the config file. 145:[ 20.257] (EE) 147:[ 20.257] (EE) no screens found(EE)
Booted up kernel-3.17.6-300.fc21.x86_64 OK.