Do you have a more complete schematic?
Because something doesn't seem right ...



The 555 part is to make IR transmitters flash at 38.5KHz.
The way that 555 is set-up, it's NOT an astable multivibrator. (oscillator)

Is it connected to the PIC?
And if so, is that connection going to pin 7 of the 555?

Pin 7 is the "Discharge" output from the 555. It should be tied to the 1nF capacitor via another resistor that's in series with the 15K resistor.

If you have it connected to an OUTPUT from the PIC, it may cause the PIC to continually reset due to conflicting OUTPUTs drawing too much current.

If you want to modulate a 38khz signal from the 555, it needs to be set-up as an "astable multivibrator" and the signal from the PIC should go to pin 4 (reset).