Splinter Cell guards know everything. Possible to fix?
Well, first of all there are a few things that could be happening:
You're not in the dark. If you're not in the dark in most cases you're going to be instantly caught whenever... (read point 2)
You are loud. NPCs are attracted to noise. They proceed to identify what the noise was (A sticky cam, Sam walking, a rock, a bottle). Once that's done they act accordingly (some try to hide, some fire at you, some run to alarms). If Sam is the one making noise check point 1.
With that being said, there's are indeed cheats, but unfortunally only for the PC version. You can read up on how to set them here.
The cheat you want to use in this case is invisible, which makes it so NPCs (guards) cannot see you. They can however still hear you. You can also be spotted by cameras.