After a fresh clean install of lxqt :


cat /var/log/Xorg.0.log
[    38.142] (--) Log file renamed from "/var/log/Xorg.pid-1998.log" to "/var/log/Xorg.0.log"
[    38.143] 
X.Org X Server 1.18.4
Release Date: 2016-07-19
[    38.143] X Protocol Version 11, Revision 0
[    38.143] Build Operating System: ecosse 4.4.26-server-1.mga5 
[    38.143] Current Operating System: Linux localhost 4.8.6-desktop-1.mga6 #1 SMP Mon Oct 31 14:20:31 UTC 2016 i686
[    38.144] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.8.6-desktop-1.mga6 root=UUID=7caaeb27-896a-48a3-8e64-5e287d32d9a2 ro splash quiet noiswmd resume=UUID=ccbb1e71-f6a6-4686-b7ed-993e5d69cb61
[    38.144] Build Date: 06 November 2016  11:06:48AM
[    38.144] Build ID: x11-server 1.18.4-4.mga6 
[    38.144] Current version of pixman: 0.34.0
[    38.144] 	Before reporting problems, check http://bugs.mageia.org
	to make sure that you have the latest version.
[    38.144] Markers: (--) probed, (**) from config file, (==) default setting,
	(++) from command line, (!!) notice, (II) informational,
	(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[    38.145] (==) Log file: "/var/log/Xorg.0.log", Time: Sat Nov 12 19:24:22 2016
[    38.145] (==) Using config file: "/etc/X11/xorg.conf"
[    38.148] (==) Using config directory: "/etc/X11/xorg.conf.d"
[    38.148] (==) Using system config directory "/usr/share/X11/xorg.conf.d"
[    38.149] Parse error on line 3 of section InputClass in file /etc/X11/xorg.conf.d/00-keyboard.conf
	"\n" is not a valid keyword in this section.
[    38.157] (EE) Problem parsing the config file
[    38.157] (EE) Error parsing the config file
[    38.157] (EE) 
Fatal server error:
[    38.157] (EE) no screens found(EE) 
[    38.157] (EE) 
Please consult the Mageia support 
	 at http://bugs.mageia.org
 for help. 
[    38.157] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[    38.157] (EE) 
[    38.157] (EE) Server terminated with error (1). Closing log file.

in fact /etc/X11/xorg.conf.d/00-keyboard.conf is badly written
with for example : Option "XkbModel" "pc105"\nEndSection"
editing the file with vi and changing all \n solved the problem