What are the main scenes/act in Hamlet that expresses the theme of Money? & how is it represented in the play?
Without the text directly in front of me, the best I can do for you is discuss some of the specific events of the play that point towards the topic you're discussing. This will answer the second part of your question--you'll have to do a little bit of searching on e-Notes or your book to find the specific Act and Scene, unless I happen to remember it.
First off, to clarify, money alone isn't a theme. Themes take a stance of some kind. What about money? Is it justifiable to commit murder to attain it? That kind of question is more along the lines of a theme. How far are we willing to go to feel secure with our wealth?
If this is more the theme that you are indicating, then I would suggest looking at a few key moments in the play. Somewhere around Act 3 (it may have been 4, actually), Claudius takes a moment to attempt to pray and show remorse for his decisions to murder his brother and attain the throne through his sinful decisions. He knows that his attempts to pray and ask forgiveness are half-hearted, however, because he is not willing to announce the evil he has committed and give up the fruits of his sins. While it may be possible to bribe an earthly judge (and this notion of bribing justice to look the other way fits into the theme you brought up), one cannot bribe G-d. Claudius' final thoughts echo this notion that no amount of money can make up for sin: "My words fly up, my thoughts remain below, / Words without thoughts never to heaven go."
Another indicator that one's need for wealth or status can eclipse one's moral judgment was in Claudius's decision not to warn Gertrude that the cup she was about to drink was filled with poison. He would rather lose everything dear to him than admit his errors, which would cost him his throne. This last example came from Act V, scene 2.