Problem with frames

So I have an asset, a block, I turn that block into a symbol 

I place the block to the left of the screen at frame one

I then go to frame 5 and place the block to the right of the screen. A frame is not created

Ok start again.

So I have an asset, a block, I turn that block into a symbol 

I place the block to the left of the screen at frame one

THIS time I create a key frame at frame 5 and on that frame move the block to the right. The only result is that the block is duplicated (i'll call the new block block B and the first block on frame 1 block A). If I delete block A on frame 5, it is deleted throughout the animation and no longer appears on frame 1. 

Why is it doing this? I just want a simple animation of a block moving across the screen yet it wont let me animate the asset, it just duplicates it. Any ideas?