You absolutely shouldn't make your background out of hundreds of sprites. This could literally be done with one single tiled background. And would save you a lot of performance.
I understand you are new to Construct and probably relied on the individual background sprites for creation and positioning of the blocks. This is entirely not necessary and can be done with a little math easily.
Basically like this: floor(MouseX(Y)/gridsize)*gridsize
And maybe add the width/height of the block divided by 2 to account for a centered hotspot.
Also your event sheet is generally very bloated. The way your are using the variable 'bc' and toggle groups is over-complicated I'm afraid. Actually reminds me a little of my first steps with Construct, so it's nothing to worry about.
As a general advice I would say try to use the function object, think about families and naming conventions for different objects of the same type. If you want to, I can give you a quick edit of your cap, with a majorly reduced event count. But still working the same, of course.
Oh, another quick hint: try to find better file hosters than megaupload and co. Because forum users generally don't like to have to click multiple times and having to wait, just to get a small file. People will be more likely to download your stuff if you put it on easily accessible services like Dropbox or Box.net.