Sorry to be a putz, but Im just wondering, is the idea to play DC, finish it, then BDC finish that and then play RDC?
AND, Im having a hard time finding something to destroy the boards boarding up the shield door. I cant imagine going on to BDC or RDC without the bloody shields...
That is not the only way to get a shield. There are three ways in total. Also, I believe there is a thread on this already, go check there.
You do not have to play the levels in any particular order unless halted by the need for an item. So you're free to galavant about in any order you can find which is possible. It is not designed to be easiest by doing DC before BDC and RtDC and vice versa. There are three ways to get the shield and fireball, so have at it in the order you like.
As for getting into Shield 1, have you really tried all possible direct approaches? Don't let the problem give you a short fuse