depending on how clogged up it is it could cause it not start, if its not spinning, it could be blocking all airflow into the engine. no air = no start

 

A seized turbo is a big restriction. I've never experienced it, but I can imagine it causing a no-start on an engine that's none-too-inclined to start anyways.

Remove the turbo and see if the engine starts. It isn't doing any good seized. That way you can at least see if the turbo is causing the no-start, or if you're having another problem.

 

I have had turbos stick on boats before and the engine still started. It won't flow much but it will idle.

 

the air and exhaust will still move through,but it will hinder the startup.Add a slightly clogged filter and your done.