Hi there.. My name is ***** ***** I will be helping you.Can you tell me what kind of cable you are using between your Fostex unit and your pc?
When you have the trim turned all the way to the left you are turning the gain down for whatever source you are recording. Which is why you can not hear your guitar on playback. Also make sure you are bouncing your mix down to stereo and not mono.. What are the position of the pan knobs? Do you have the guitar centered? or is it panned left or right?
The trim knobs/gain knob... control how loud your source is going into the fostex. You should get a nice clean signal without clipping.. Turning it all the way to the left turns it all the way down, to the right all the way up.. You want to find a happy medium. After you have recorded your tracks you can adjust the volume of each source with the faders.. The pan knobs are for panning your source left or right.. or right up the middle. I'm not really sure why your guitar track would fade out.. did it fade out at the end of the song?