dsPIC33 Simple External Interrupt problem
I see three missing things.

Missing dspic33 number??

AD1PCFGL = 0xFF, or whatever the datasheet tells you, to turn off the adc on those pins, if necessary.  ANSEL is for choosing adc input, not turning them into digital.

Input pins TRISXbits.TRISX? = 1, to turn your pin into an input.