Hi,
Best thing to do is write a totally separate simple program with a simple delay of 1 second to flash a led, making sure you do Not use the ISR in your code.
Most compiler tutorials start you off with such a simple hello world/ led flasher program
Bet that will work ok, which probably means your main code has some basic bugs in it, probably around your ISR section ..?
You do not say if your crystal is soldered in a pcb or on a breadboard ? - if on a breadboard, solder the crystal and caps together and fit two very short breadboard thickness wires to them so the assembly makes good contact with the breadboard sockets and is as close as possible to the pics pins.