I have ran across LCD that does not need an adjusting pot, the contrast pin could be connected directly to 0 volt (ground) and would work. So it is possible your instructor was using one. But not very possible! I would say this happens maybe 1 out of 100 times. You need the adjusting POT.

Questions that I am still not clear on:

1- Are you using the exact same board and LCD as your instructor?

2- Is the board and LCD a copy of the one your instructor has?

3- Did you instructor compile his/her program on the same computer you are using? ( this is to test the LVP config)

4- What does you instructor say about the problem?

Please provide a drawing showing how the LCD is connected (draw it on paper and scan it if you have to)

Go here http://www.microengineeringlabs.com/support/index.htm and you and the instructor look at the manual under LCDOUT, it shows the correct way to wire a LCD using PORTA as a default. I am not saying to use PORTA, but look at how the contrast is set up.