Kay, if you've put the cube with cards together then all you need is to enter the door with the circle & dot in the center. That's what that cube is for. The door is in the kitchen/dining room. Upstairs is the final piece of the note on a door. If you can't exit you probably are missing a piece of the note. If you have all pieces of the torn note, click on them each individually & they will assemble. This is your ticket out!
Safc, try going in the door left of the dresser with the radio on it in the first hallway room. You might find more things in there that will help you. You don't put the cube together. You just find the pieces & it will assemble itself. The first cube requires 4 pieces. The first piece you found in the hallway room & 3 more from the living room. Do you want a spoiler where the pieces are?