thanks for the hint
it is a lenovo i7 desktop with 8gb ram and nvidia card with 1gb
nasser@nasser-ThinkCentre-M93p:~$ xrandr
Screen 0: minimum 320 x 200, current 1360 x 768, maximum 16384 x 16384
DVI-I-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left...