Darrel most likely hit the nail on the head. Sounds like some odd hardware problem, or a
bad connection.

Troubleshoot things one-at-a-time, and just setup a simple loop shooting serial data to
your PC serial port until you get the serial com thing working.

If it goes-like-splat, then you know there's a bad connection - or maybe even a problem
with your PC serial port.

Note: It might even be a problem with the PIC itself if the A/D is foo-bar. The ADCIN library
function is a blocking type with;

adcinloop
btfsc ADCON0, GO_DONE ; Wait for conversion to complete
goto adcinloop

If ADCON0, GO_DONE never gets cleared, it's a sit & spin function call...;o}