Choose a pistol from your inventory and proceed towards the stairs. It's EXTREMELY important that you pick up an explosive bottle (screen). Open your inventory and use the bottle on the pistol to create fire bullets.
Try getting closer to the main entrance to the castle. You should notice that a fissure monster has appeared in this area. Obviously you will have to defeat it before it gets too close (screen). It shouldn't be a problem, as long as you're using fire bullets.
Equip yourself with an explosive bottle. If you don't have any bottles, try looking around and you'll find plenty of those. Aim at the main door to the castle and destroy it a well-placed bottle (screen). Proceed to that location.
Once you're inside the mansion, it's extremely important that you read a new text message from Sarah. You'll find out that you'll have to improve your spectral sight to at least 30 points. This means you'll have to destroy a sufficient number of roots of evil. Check Optional: Roots of Evil - Part 1 for additional info on how to find the roots and how to destroy them properly. If you have 30 points or more (you'll receive confirmation from Sarah and you can check this in the main menu of your cell phone), you will be allowed to go back to completing the main goal. Go to Scene 4 - Par t 2 and continue playing.