Writers Block

I’ve got really bad writers block of a sort, I have a story idea, I know how I am going to start it, heck I even know what the first couple of sentences are, I just can’t bring myself to start writing it.

The story is a thriller that starts when a one night stand goes horribly wrong, at least I think it’s a thriller, I’m not sure yet.
Regardless I should be able to start it, I know what happens in the first chapter, why can’t I at least write that?

I think it’s because the Idea is still in gestation, at least that’s my excuse. I’m going to let it gestate for a little bit longer, but I might take some notes so I don’t forget where it’s going.