What happens when you are unable to move in Stratego?
Straight from page 5 of the rules:


  Note: if a player cannot move a piece or strike in his/her turn, they must give up and declare their opponent the winner.


So, yeah, don't set up your bombs and flags in a manner that prevents most of your troops from being movable without the bombs being removed by an opposing miner (that's actually another easily-missed point - the only way for a bomb to leave the board is if a miner hits it. Any other piece is simply lost while the bomb stays). You will be forced to forfeit if you cannot make any move at all.