I don't use ISIS/Proteus, but as per your configuration fuses, you must tie you MCLR pin to Vdd... make sure it is done.

Another thing... It's nogt a bad Idea to finish your program with an endless loop, so the LED will stay on.

I bet this will work, if you haven't tied you MCLR pin to Vdd
Code:
    LIST P=16F676
    #include <p16F676.inc>
    __CONFIG   _CP_OFF & _CPD_OFF & _BODEN_OFF & _MCLRE_OFF & _WDT_OFF & _PWRTE_ON & _INTRC_OSC_NOCLKOUT
    
    CLRF    PORTC
    BSF    STATUS,RP0
    CLRF    TRISC
    CLRF    ANSEL
    BCF    STATUS,RP0
    BSF    PORTC,4
    BSF    PORTC,5
    BSF    PORTC,2
    BSF    PORTC,3
    goto $
    END
And from what I do remember of my venture with ISIS, you need to specify the osc speed... set it to 4MHz and try the above without specifying the configuration word value. If it's still not working, tie your MCLR pin to Vdd. Ought to work ... or throw away ISIS