My lcd arrived today and i saw that when i connect the backlight pins (A and K) to GND and +5V, the backlight turns on, but i cannot control it with the potentiometer. The wiring seems fine (ive checked and rechecked). Also, the 'hello world' sketch from the arduino website does not seem to be working at all. Any suggestions?
You need to check a few things.
1) What voltage rating is the LCD? Most LCD displays require +5V power supply.
2) What voltage is the processor on your Arduino board running at? These can be either 3.3V or 5V.
If your Arduino board is running at 3.3V and you are trying to run a 5V LDS display from it without using level conversion, it probably won't work.
3) Does the display change at all as you rotate the contrast pot? FWIW - the voltage on the contrast line is usually fairly close to ground.
4) How have you connected the display to the Arduino? You need a minimum of 6 lines: data lines 4-7 plus EN & RS. Just connect the R/W line from the LCD to ground for now.
5) Is your LCD rated for operation at cold temperature? If so, you may need to bring the contrast line below ground (negative). It doesn't need to be much below ground and you should still see something on the display with the contrast voltage set to 0V - but you may need to do this if you can't get enough contrast on the display when you get it working.
6) Is your Arduino sketch known-good working code?
7) Are you actually getting your code into the Arduino? Maybe do a flashing LED from one of the port pins to ensure that your programming environment is working.