Whenever I download a tab at least one of the channels doesn't work. None work on my hand of blood tab!
I would make sure the channels have the volume turned up, and configured properly in the program, then i would check your speakers. If this is consistently the problem, i would send an e-mail to Guitar Pro. It could be a software glitch.
click MIX TABLE at the beginning of the song on the track that doesnt work. Click VOLUME and turn it up full. click OK.
maybe your volume of the se- synthesizer is down click at the start bar of windows to set it up
I always have to click on each track and select from MIDI to RSE, try that.