Alright, earlier today I was browsing around on some forums, and found the answer: the speed of Sam Fisher is moving at is how fast the tumblers move, so if you're going really slowly to stealth past some enemies, the tumblers won't move at all.

Solution: Go to crack the same. When you see the tumblers on the screen, scroll the middle-mouse wheel up, or whatever the speed-increase button is set at. You will then be able to crack the safe. Hope this helps!

Nice man, i always thought that it was a bug in the game... now i tested it and comproved... thanks a lot!

wow thanks. i thought it was glitch too. i found out that i counld get them to move if holding up arrow as well as diretion but this makes it much easier and stops me failing on shanghei mision and makes the last mission much easier

yeah, that might work with the defusing part of the bomb too, sometimes it just moves soo slowy that might be the answer... the safe problem really pissed the hell out off me, thanks to u not anymore... but anyway... never would think about the mouse wheel!

This post is just a bump, so everyone who has this problem in the future can see the solution.

I might as well just sticky is for a while, and leave it open. Any further comments, feel free to leave them here. =)