Hello.
If you commented out HSERIN in the ISR then you're not clearing interrupt flag, therefore constantly looping between main routine and the ISR. Also, I would advise to read RCREG first then toggle portb.5. But it would be much better to pick up a complete package and deal with it in the main routine.

Out of curiosity:
DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h ' Enable transmit, BRGH = 0
DEFINE HSER_SPBRG 12 ' 4800 Baud @ 0.17%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

RCSTA = $90 ' Enable serial port & continuous receive
TXSTA = $20 ' Enable transmit, BRGH = 0
SPBRG = 12 ' 4800 Baud @ 0.17%
Why doing same thing twice?