Vauxhall Zafira wont start even after replacing glow plugs?

Took my car into garage as it would not start in a morning, it just got gradually worse. They replaced 2 of the glow plugs but said the other 2 were stuck in the engine and they could not get to them. Anyway the car has come back and it still wont start, I think it maybe a different poblemm, but wont take it back to that garage. I was thinking of trying another garage that I have used in the past, but don't want another big bill saying either it should be ok now and its not or charging me loads and not finding a problem, did a seach on google and its not an uncommon problem.

Could anyone advise on my next step or even to advise the garage what to look for?

Thanks