Queen's gambit declined

We all know it is not good for black to play Nc6 in front of the c pawn in the QGD.But I want to know what should white do to take advantage. For example if 1.d4 Nf6 2.c4 e6 3.Nc3 d5 4.Bg5 Be7 5.Nf3 then 5...Nc6.

How is white in advantage?

black's light squared bishop is hemmed in and white has better attack options on the queen side

But black can place his bishop on d7 and his rook on b8.I don't see what can go wrong.    

Even if white exchanges pawns by cxd5 exd5 and then places his queen on a4 and his bishop on b5,black can play a6 to avoid the capture of the a pawn after white plays Bxc6.

even though black developes his bishop at d7, it will be basically useless because it's all blocked in and has no mobility.

Bd3 usually works fine for me, white has options, black doesn't

Quick looking at short term advantages.  Black is going to be smothered.  He can't contest the center, he has no play on either side and can only await the drop of the blade.

In the position given shouldnt it be black to move ?  I count 6 moves for white and only 5 for black. 

Yeah,its black's move in the diagram.I've revised the position again and found out that black has a much better move than Bd7. He can exchange pawns by dxc4 Bxc4 and then push b7-b6 with the fianchetto of the bishop. If he had fiest pushed on b7-b6,white would have exchanged first by cxd5 exd5 and the fianchettoed bishop's diagonal would be blocked.