2001 Vauxhall Astra cutting out

Hi there, was wondering if anyone has heard of this problem before, I have a vauxhall astra 1.6 sxi 16v, and all of a sudden it has been cutting out on the bypass or motorway, if I am driving at a constant speed on the bypass, i.E. 60mph the car judders then cuts out and wont start by the the key, it has to be bump started.
i dont even know where to start with it,
the car has just had a major service 3000 miles ago, including timing belt,
iv checked for fault codes and there are none,
i have also blocked off the egr valve with the modified gasket from vauxhall.
i dont understand what os happening, and would appriciate some help.

thanks you

mark :)