long shot here. But what up pipe you using. Is there any flexi joints before the turbo? I had similar problems a while ago. My up pipe flexi joint burst a little and the turbo in turn, ate it! Waste gate was stuck open and turbo was goosed. This happend with no noises or indications at all. Just no boost or spooling noise. My car was flat as a pancake. Revs wouls built up, but very very slowly, even getting to 50mph on the by pass was basically impossible!