Thank you, although the example shown was different for me, no red blocks to get and until I posted no yellow were dropping into the centre but thankfully they now appeared and was able to do :)
I am stuck on Level 6887. I am required to remove 8 yellow blocks, which never show. It is just a random blowing up bombs to possibly remove a hidden yellow one. It is just a matter of luck, not skill and could take months! any hints?