Please don't feel insulted if i'm about to state the obvious - but you never know and its easy to overlook the simple things sometimes. something i'm all too guilty of doing!
Have you made sure the Sustain and Release are all the way up on the AMP Envelope. Set the first two sliders (attack and decay) all the way down, and the last two (sus, rel) all up.
Check your Filter cut-off is fully open and resonance is down (bypass the filter)
Turn all OSCs down and only Audio slider up.
Make sure no LFO amp/filter action is happening.
Press and hold a key while the audio is being sent. (use the sequencer hold function and swith the sequencer/arp to play mode to aviod having to hold the key down)
Still nothing?