1. [In the bedroom] Pick up a instruction flyer for the safety box which is located inside a garbage bin between the desk and the green couch. Click on the brown recliner. (Nothing will happen at this point, but I think it may be necessary in order to trigger a flag later on)

2. [Kitchen/Living room] Click on the little space between the chair and the sideboard. there you will find a safety box. Look at the glass table, and click on the notebook. (BTW, the notebook says "I've been becoming very forgetful lately - I'm even forgetting where I put the key to my diary. Is it too lame to put the key under the plants?") Go to the kitchen part of the room and pick up the torch from the stovetop, and take the poster from the opposite wall along with the thumbtacks.

3. [Corridor] Click on the plant located at the end of the corridor, pick up the key.

4. [Bedroom] Click on the diary, which can be found at the bookcase right next to the desk. Unlock the diary and then click on the diary at least 7 times. 

5. [The room with keypad] Enter the room by pressing 
233

. Pick up a videotape by the stereo, a CD from the glass shelf thingy, and a pair of batteries underneath a chair. Enter the door (the one without the keypad), go near the window-like thingy, click on it, and then click on the poster from your inventory. Now, the poster is posted on the wall. Go back to the door, and click on the switch right next to the door, turn on the torch and go back to the window-like thingy where you just put the poster on, and turn off the torch. (now, the poster spits out the secret message saying "I left a memo in the little opening on the chair"). Turn the torch back on, and go back to where you came from, get out of the room.

6. [Bedroom] Click on the safety box from your inventory while you are facing the bed. (When you picked up the box, there should've been a message indicating the "I should be trying opening this where I feel very comfortable", and the spot right in front of the bed is indicated as the spot that "I feel very comfortable"). Just follow the instruction illustrated in the flyer that you have picked up from the garbage bin earlier but in the reverse order. Now you should have a battery for the laptop. Click on the brown recliner, and you should find a piece of paper, which is happen to be a memo for the PC password, and pick it up. 
Now, click on the laptop battery while you are facing to the laptop. Click on the laptop, and then you should see two icons shown on the desktop. Make sure to click on the CD from your inventory, then you should now have the third icon, and that's where you want to type the password in.

3ef5e5yi

Now you should be prompted with the password to the "music room" 

39039

7. [Kitchen/Living room] facing the TV, click on the videotape from your inventory. There you should get a sequence of the steps that you will need at the "music room".

8. [The room with keypad lock] enter the room and press the entry code for the music room. Now you should see a floor with grid-like feature. You will want to click on the floor in the following order: second grid from the left, second grid from the left, third grid, 1st grid, 4th grid 4th grid and 2nd grid, then voila, you should be able to open the door!