I have read that someone else was suffering this same problem, but no one seemed to get back to him on the matter on how to resolve this issue, and that post was from 2009. Hoping someone may be able to help me. I can't get past the first level of the game since it won't allow me to pick the first lock. It just locks up at the door and nothing happens. Does anyone know the reason for this?

the game hates when vsync is turned off, make sure you aren't forcing this setting in any way. also, try this.

Thanks for the quick reply, I'm afraid turning on Vsync as well as downloading the file you linked me didn't correct the problem, I am still unable to get past that tutorial levels lockpicking point. I've even tried tinkering around with lowering the graphical settings and setting them to default, and just anything to try and possibly correct the problem. No luck I'm afraid.

try to report everything in the TTLG sneaky update topic.

I have the same problem. It's really annoying.
Did you find a solution?

EDIT: I found the solution here.
It works very well, thanks to Stayce!

Hey I'm afraid I simply just gave up on playing it on PC. I have the game on the original Xbox which I have hooked up to one of my TV's, so I am just gonna play it on there when I decide to get around to it, sorry for not posting more on it.

Hey man, just a heads up on the xbox version: The game contains a gamebreaking bug that defaults the difficulty to normal no matter what difficulty you pick. The PC version was quickly patched but of course that was not possible on consoles at that time so was left like that. Unfortunatly normal on thief 3 is REALLY easy. So make of that what you will :) I thought the game was super easy on hard until I learnt of that bug.

Also are you playing on 360 or original xbox. Playing 360 has a weird glitch where EVERY lightsource in the level can be seen through walls so obscures vision. Gets pretty bad later on where there can be 15 torches in a level.

Oh right on man, thanks for the heads up. I'm just playing it for the original Xbox, didn't know they released it on 360 haha

I've just released a new version of my "Sneaky Upgrade" Thief 3 patch, which will hopefully fix this and similar issues. I'm very interested in feedback, especially if you have a monitor capable of refresh rates above 100 Hz and vsync enabled.

On my laptop, version 6 of the GOG installer seems to force-disable vsync.That could probably make this problem affect more people.

Edit: Other interesting highlights from the 1.1.3.x version are somewhat faster level loading and that the chosen difficulty level is now active in the City hub...