I have owned this game since it's inception and the two previous and the one after. This game is broken now and unplayable. Every time I load it and go through training it gets stuck when you need to pick the lock. You right click to pick the lock and it acts like it is going to zoom in and bring up the GUI for the lockpick and then it sits in that position for a minute and then returns to regular view. I messed with it for about an hour and finally got it to come up once... then when I got to the first ladder to climb it did the same thing. It won't let you mount the ladder normally. I fidgeted with that for another 20 minutes and finally got up it. That is a fairly short ladder and I thought it might just be that mission. I completed that and went to the next mission and the first ladder I need to climb is tall and I am simply unable to climb it. I have fought with it for an hour and cannot climb the ladder seems that the whole game is broken and unplayable now. I hope there is someone that can fix this. I miss this game and wanted to introduce my kids to it.

This is an old known bug with the game that occurs when you play at frame rates higher than 60fps. Restrict it to 60 or lower and you will be able to pick locks and use ladders reliably again.

I recommend installing the Sneaky Upgrade mod, which does this as well as fixing a number of bugs and stitching the notoriously small levels together so there are fewer loading screens.

https://www.ttlg.com/forums/showthread.php?t=138607

don't even try to run the game without it nowadays.

BEAUTIFUL! THANKS! I will give it a shot! I really appreciate you responding so quickly. I thought I was just gonna be out of luck. My kids are gonna love this game! Thanks again and have a great day! Thanks so much for the Link! I really appreciate you guys taking the time to help a fellow Taffer out!

Now you need to be sneaky to install the sneaky upgrade.

Try disabling Vsync in game and forcing it in the settings of your graphic card. What's the problem with Microsoft Defender? Does it prevent you from downloading the patch or from installing it?