Scary moments in PC games, hmm, let me think:
- The haunted house in Vampire: Bloodlines
- The first turn outside the Skyranger in XCom : Ufo Defense when your team is shot at.
- The first time you encounter a DGN (Dragon in it's Lair) in dnd (Yes, this is an early ASCII dungeon crawler)
- The first time in Half Life 2 when you encounter the toxic head crabs.

You picked the wrong moment from F.E.A.R. The ladder jumpscare is probably the scariest jumpscare in the whole game. It just comes out of nowhere, when you don't even expect anything to fit in there.

as mentioned before, it's really individual - maybe you're a fan of horror, seen many ultrascary movies and love Outlast and games like that... me, I hate them :) I prefer psychological scare, not jumpscares, ghosts or ugly monsters, so Phantasmagoria is straight up my alley... Phantasmagoria 2 is also very good in my opinion, even though even fans of the first games usually say it's bad :D

You, sir, are a gentleman and a scholar. You got that exactly right.

i actually am much, MUCH more scared bout that drm ridden game that gog is still selling without any warning of its customers! selling f.e.a.r., but fck drm! right gog?

Thief definitely deserves to be here. Not just obvious levels like Down in the Bonehoard, but unexpected moments in levels like Song of the Caverns where you pass through a water area slowly to avoid the Craymen then out of nowhere a large "whomp" comes from a boulder falling into the water right beyond you. Better horror games than most "proper" horror games.

Clive Barkers Undying.... just saying

Amnesia: The Dark Descent: The sacrifice flashback scene in the Choir entrance corridor, waking up after with sanity completely drained and the image of hanging corpses all over.

S.T.A.L.K.E.R. Shadow of Chernobyl: The bloodsucker that laid a trap for you in the small house outside the bandit camp in the Dark Valley.

Metro 2033 Redux: Entering the abandoned house shortly before meeting with Bourbon in the Dead City level, seeing the dark silhouette of a hanged man and when going out, the apparition of two kids for an instant. The final corridor in the Black Station level.

I remember being a nervous wreck the first time I played Alien vs. Predator 2 on that first marine mission where you don't actually fight anything, but the tension just builds and builds.

Yes that was very well done.

Aliens TC for Doom.
Check those corners!

Afraid of Monsters (Director's Cut) - Not a classic PC Game, but this was a scary MOD for HL. Like being in a nightmare. Scary moments: Almost everything, but I remember hearing a knock on one of the doors (won't say when/where for spoilers).

F.E.A.R. - This was a different kind of scary. Not the cheap monster/jump-scare scary. This game is a masterpiece and deserves a spot in the Best Games Ever list. Scary moment: Seeing someone peak around a corner at you at the right moment, or being alone in one of labs when you get another whiff of the backstory.

The Ocean Hotel im Vampires the Masquarade: Bloodlines! scary as Hell and one of the best Level in a Computergame ever.

"DIVE! DIVE! DIVE! Hit your burners, pilot!"

The one that always comes to mind is X-COM UFO Defense...there were actually a few that scared the heck out of me:

-the first ground mission - because you didn't know what to expect (and the spooky music didn't help any, either).

-the first time you were sniped by an alien from the shadows - you set your squad up to, what you think is, the perfect defense posture only to have a plasma bolt come out of no where and kill your squaddie

-the first terror mission - the spooky music, again, plus the invisible shots being fired in the distance and the screams of the civilians all make this a very scary picture

-the first terror mission with Chrysalids - having some creepy black creature walk a thousand steps across the screen and then turn your squaddie into an evil zombie...and if that weren't enough, having to kill your former squad mate only to have another creepy black creature spring from his corpse. Now that was scary! :P