Most probably once when you chose to delete some blocks, a dialog box came up saying something like "Are you really sure to delete these blocks?". Also there was a check box on the bottom like this "Don't allow dialog boxes to appear anymore" or similar. It seems to be, you checked that checkbox. Now, whenever you hit the delete key, it does nothing. The dialog box no longer shows up.
To get that dialog box back again, type chrome://settings/ in the browser's URL box and get then press "reset settings". And next time you get that option again, do not check that checkbox...
PS: It does not look like you have used the forums yet, as a search using the search box above would have returned several threads about this topic.
Advice: Before posting, it's a good idea to search in this forum. Many others have likely run into problems similar to yours. How to search see screenshot.