https://i.imgur.com/4RKYYO8.png

Bascially I've found 2 brass keys, but I cannot use them on any keyholes, it gives me a "failure" sound.

Are you still having problems with this? Have you tested opening the door after using the key on the keyhole regardless of the sound (successful unlock or wrong key noise - I'm assuming this is what you mean by failure noise)?

Does the brass key work on any of the other keyholes (the locked door two squares north of the red marker on your map, the locked door to the north east tower, the locked door in room you got the journal in).

Edit: Sorry, you said "keyholes" (plural), implying you can't open any door. Can you describe the "failure" sound? The correct key used on a keyhole has a pretty clear "unlock" sound for when it works (duh), and more of a "key jingle" sound for when the wrong key is used. Are either of these the sound?

Also (just to confirm), when you're going to unlock the door... you're facing the keyhole, open your inventory, select the key, move the key over the keyhole with your mouse, and left click right? Forgive me for asking a fairly basic question like this but I've seen one or two new players go about this the wrong way.

I was just assuming using key = auto opening doors, like in any other dungeon crawler.

So, no, no problem anymore