Here's a few notes from me. I'm a complete newb to Construct 2, so there are probably better ways to do everything than the way I may suggest! <img src="smileys/smiley2.gif" border="0" align="middle" />
First, I noticed that your Background image was on the main layer. I moved it to the "Background" layer since I figured it belonged there. <img src="smileys/smiley2.gif" border="0" align="middle" />
Secondly, I noticed that your block sprites are 32x32 pixels, yet in your level they're only 25x25? I don't know if that's intentional or not, but I thought I'd mention it just in case. Also with your level layout, it's usually easier to line things up if you use the snap to grid function. (Which is another reason I mentioned the size difference from 32x32 to 25x25.)
There were also some hidden "landing_objects" placed under some of your coin blocks. I removed them since they were causing problems with the player hitting the coin boxes.
Lastly, I changed the event where the player hits the box so that it changes to the "blankblock" without you having to place both in the scene overlapping each other.
There's still some things that need to be worked out, but hopefully this gets you going in the direction you wanted to go! <img src="smileys/smiley1.gif" border="0" align="middle" />