Does "hadn't" exist?

I don't think you would ever use hadn't in first person conversation.

But what about third person, in books for example?

If Jimmy hadn't set his alarm, he would of been late for school ?

is hadn't just a contraction of had not? so see if you can use "had not" in context

such as "I had not got laid since yesterday"...

Doesnt feel right imho.

Why not?

"I'd be screwed if I had not used Blackboard" = "I'd be screwed if I hadn't used Blackboard."

Perfectly fine and acceptable. You probably use it without realising.

Sometimes I might switch it round with a "had I not", but it's fine.

Why not?

"I'd be screwed if I had not used Blackboard" = "I'd be screwed if I hadn't used Blackboard."

Perfectly fine and acceptable. You probably use it without realising.

Sometimes I might switch it round with a "had I not", but it's fine.