It's a little difficult to tell for certain without punctuation or context, but...
The first one almost certainly means "[I'm] Surprised" (or something like "You startled me").
The second one probably means something like "Don't Surprise me!" (As in "Don't sneak up on me!", etc.) For example, parents often say to children "~するじゃないのよ！" to mean "Don't ~". (This is colloquial).
For your second question, again, without context, it's a bit difficult to answer, but "びっくりしたじゃないか" would typically be in reference to something that just happened, to express shock like "Well that was surprising, wasn't it!"
"びっくりするじゃないか?" is more like "[That kind of thing] would surprise anyone, right?", and would more likely be used express surprise in context of something you heard on the news, etc., or suppose that it would be surprising to people in general.