Distortion & low signal

Question

I have purchased a second-hand Fostex FD-4, set it up (normal mode) as per manual instructions. On attempting to record/monitor a guitar track the gutar signal is coming through at a) an extremely low level- LEDs only go up one or two with guitar at full volume & input/master faders up to 7/8 and b) distorted.This has happened with both an electric and electric-acoustic guitar, I have tried swapping leads and all four input channels (including the two that have high/mid/low switches) I have tried lowering instrument volume and pretty much everything else I can think of.The manual lacks a troubleshooting section and I've gone through the setup step by step.Help!