photoshop blacks

What happened to the colour black?

O.K. as I stated in my last post, I am not a graphic designer, and that became quite apparent when I uploaded the poster on my last blog entry. In photoshop the blacks looked really good and deep, but once I put it up here it all looks kind of desaturated. When I reopen it in photoshop it still looks all nice and black. What's the story? Anyone?