but the word "value" always flickering , why ?
Probably because something is overwriting it or clearing the screen, then you re-print the VALUE on the LCD...

as i said before , whene there is 5V , i don't want any bars , there must be full bars at 3.9V
Simple math
Minimum = 5V (1023 ADC counts)
Maximum = 3.9V (798 ADC counts)
Spread = 1.1V (225 counts)
raw = 1024 - raw 'flips the value upside-down
raw = raw / 14 '14 counts per box, assuming 16 boxes
Surely you can do something with that...