Possible causes,
No/wrong crystal or no/wrong capacitors.
MCLR not tied high.
RB3 not tied high as LVP not turned off.
No power.
Pic not programmed.
Etc.
try erasing the pic, when done check the buffer of the pic if it is blank all 0xff then try to fill the buffer with some hex read it again if it is there as u put it, this will confirm if you are able to program the pic