PIC16f676 external crystal issue

[arslan43711]

Hi,
I am using pic16f676 to blink the (for example) led now when i select the internal oscillator led blinks perfectly fine but when I change the oscillator to external XT (my crystal is 4 MHz) it does not works. While crystal has 33pF caps with its legs. Than i changed the caps to 22pF it worked again for 24hr then it stop working again . Now I changed the XT in configuration bits to HS it started working again. Can any one explain what might me the cause?