Question

had it not been for和were it not for有什么区别

Answer 1

had it not been for和were it not for区别为：假设不同、情况不同、用法不同。

一、假设不同

1、had it not been for：had it not been for是对过去进行假设。

2、were it not for：were it not for是对现在或是将来进行假设。

二、情况不同

1、had it not been for：had it not been for用于与现在相对应的情况。

2、were it not for：were it not for用于与现在相反的情况。

三、用法不同

1、had it not been for：Had it not been for their help,we wouldn't have succeeded.如果没有他们的帮助，我们就不可能取得成功。

2、were it not for：Were he to leave tomorrow, he would get there for holiday.如果他明天就走，他就有可能到达‍那儿度假。

Answer 2

had it not been for和were it not for 都是英语的虚拟语气在条件句中的表达，都省去了if。
前者是表达与过去事实相反，后者是表达与现在或与将来事实可能相反。