Hi Lerameur!
As I was answering your post my second question was answered, you are using a 7805. So the next question would be did you install the .1mfd and some other value capacitors on the output of the 7805? The reason I ask is that 7805's as well as other voltage regulators will oscillate if there are no capacitors. Once the oscillations start eveything will act "spritual" (technical term) as the PIC is basically being powered by a form of AC and not pure DC! Best, Ed