According to the datasheet ( http://ww1.microchip.com/downloads/e...doc/39598e.pdf ) pin 4 is MCLR - from the schematic it seems you have pin 3 (RA4) pulled high via a resistor.

You also don't show any timing crystal, so assume you are using the internal osc

The PIC16F818/819 devices include an internal
oscillator block which generates two different clock
signals; either can be used as the system’s clock
source. This can eliminate the need for external
oscillator circuits on the OSC1 and/or OSC2 pins.
The main output (INTOSC) is an 8 MHz clock source
which can be used to directly drive the system clock. It
also drives the INTOSC postscaler which can provide a
range of clock frequencies from 125 kHz to 4 M
Therefore you might need to configure the PIC for internal OSC

FOSC2:FOSC0: Oscillator Selection bits
111 = EXTRC oscillator; CLKO function on RA6/OSC2/CLKO pin
110 = EXTRC oscillator; port I/O function on RA6/OSC2/CLKO pin
101 = INTRC oscillator; CLKO function on RA6/OSC2/CLKO pin and port I/O function on
RA7/OSC1/CLKI pin
or
100 = INTRC oscillator; port I/O function on both RA6/OSC2/CLKO pin and RA7/OSC1/CLKI pin
011 = EXTCLK; port I/O function on RA6/OSC2/CLKO pin
010 = HS oscillator
001 = XT oscillator
000 = LP oscillator

Hope that helps