Have checked the cables over and over again and I find it correct.
I have heard that before.
The LCD starts and the backlight shows, but not the letters.
Sometimes the white boxes flashes a millisec or so, then disappears.
Are you using a current limiting resistor with your backlight?
I got the 10K potentiometer. And I have tried with and without it, same result.
I also cant change the contrast with the potentiometer coupled on.
You must use the potentiometer and you must get the contrast working before you proceed any further.
If you can't get a row of boxes to appear then you are wasting your time trying to display any text.
Ive checked the outputvoltage on it,and it works!
Explain what voltage(s) you measured and why you think it works. When it really works you will be able to see a row of boxes on the screen.
We really can't give more help without more information.
Don