There's no difference, that's not the problem.
I simulated the program in proteus and it works fine.
I have 5 volts on Vdd (pins 11, 32), 5v on MCLR when I start the microcontroller after programming, PGD and PGC are linked to the pins 40 and 39 like they should be.
The microcontroller is ok because I tested it at school with another development board from my professor.
I even replaced the oscilator with another one but it's the same thing.
Something is wrong with the programming I think..
thanks