Kate, you break the glass with the baseball bat inside the right hand side of the cabinet. Hope this helps you.
EDIT.......................
OH MY! The lazer mirror puzzles are not easy. I again humbled myself and asked my beloved hubby to do it for me I could only do one out of 4 puzzles and he had victory. But he never wants to see another mirror lazer puzzle again.

I tried so hard to take a screen shot for you all, but for some reason I just ended up with a black box. I am so sorry I can't tell you how to do it, he just figured out it would be the least likely way to hit the targets and it worked.
I will try and explain what he did. above the first set of 4 balls, he placed the bar above the lights and the bar below the lights.
lazer will reflect off the top bar and goes through the first light. It will reflect back up to the 2nd light and it bounces off the top bar again, back down to the bottom through the 3rd light and it reflects off the bottom bar again through the 4th light. You do the exact same thing with the other two sets of lights. This is for the last puzzle and the toughest one.
Once you get the first set of lights, you will see you have to get 2 reflections off each bar. It gets easier once you see how the first set is done and just copy the same moves.
Hope this helps someone.
Good luck
Sherryah
EDIT UPDATE.................
I am stuck in chapt. 22 at the wedding and gretchen, don't understand what they want me to do. Where the hint is lighting up is a vase of flowers with a rose, but when I click on it nothing happens. I am suppose to match the image with the lost Gretchen with the real Gretchen and Einbock has fainted once again. Anyone who has finished the game please tell me how to do this? thanks in advance.
EDIT UPDATE YES AGAIN!..........................
Never mind I don't need help because I found out the answer is in the Proffessor's open eye.

I WON the game!
Really loved the game even though I paid full price and BFG gets it 2 days later! It was worth the price and I loved the voices and story line.
Also Bitty Kitty, the history puzzle when your stuck you just keep hitting hints they are unlimited. You have to watch carefully though because it has a cursor that runs through the wrong order very quickly. hope this helps you.