You locked yourself out!
Walk to the right and use the blue door to enter the block of flats. Climb the stairs and use the door in the middle to talk to your grandmother. She won’t give you the key and she won’t let you in. She’s angry.
Walk down the stairs and all the way to the left to enter the alley. Use the box to find a BROKEN AMULET. Talk to the bum and ask him for help. He’ll suggest to go to your grandma and when you tell him you already did, you should go to Melt and Drake. If all else fails you can also try Davy’s room. The window is open.
Walk to the right and go north at the postoffice and pizza shop. Talk to Grim Reaper and tell him about grandma. He can help you but wants the Amulet of Red Dot. Walk to the left and walk through the white gate. Talk to Melt but his options are not really feasible. Walk to the right inside the house and talk to Drake. He’ll give you some herbal TEA to relax.
Use the box in the lower left corner of the room to find a tube of GLUE. On the right side is a crack in the wall. Use the crack to find another BROKEN AMULET. Use the two pieces of amulet together in your inventory. Use the superglue on the combined pieces to make it one again. Leave the house on the left and walk through the gate. Walk to the right until you meet Grim again. Give the amulet to Grim and together you’ll visit grandmother to get the key.
Game source: A copy of the game was found here on the internet.