Think I've been everywhere and got everything, but the code I've worked out doesn't open the safe.
Warning Spoiler
Picked up the pen
Found cassette tape
Found scrap of paper - - Open Triangle = 4
Picked up darts
Found number sequence behind bed 9, 12, (Filled Square), 20, 1. Filled Square = 5 (sequence on dart board).
Found coin
Found book under bed
Found diagram on top shelf
Used cassette with diagram - - Open Star = 3
Taken picture out of frame
Used picture to work out book code - - Circle = 2
Found Silver key
Found Tweezers in Silver drawer
Picked up Gold Key
Found Knife in Gold Drawer
Used coin to take cover off lamp unit on shelf
Picked up bulb
Placed bulb in desk lamp
Turned off main light
Found equations; Filled Star - Filled Star = Filled Star. Filled Star = 0 Circle + Filled Square = Open Square. Open Square = 7 (2+5) Open Triangle - Open Star = Filled Triangle. Filled Triangle = 1 (4-3)
Used pen and darts on poster
Cut poster with knife
Safe code = Open Square, Filled Triangle, Open Triangle. My calculations/guesswork makes that 714, but it doesn't open the safe.