Hello,
I have integrated an arduino uno with a 128x64 graphical display, the display is JHD12864E.
Here is the Link which i have referred..
I cant change the contrast of the display. 2 days back i got a good looking lion image, although the contrast was not changing, I have used a 10k preset.
And now, after that day I have tried the same connection along with same code, but there is no image this time, Im feeling very sad.
The display is now showing all black leds.
The Lion Image was 2 days back.
and I have stuck with a black rectangle on the display..... 
This was obtained before 2 days. I was not able to change the contrast of the display while i have obtained this one..
After two days I uploaded the same code with the same connections and this is the problem i have stuck here now, and the contrast is also not changing still.
This is my second Display of my project, Im not willing to buy a new display. 
Please need help..