Hmmm it worked ok for me on xbox. I haven't played it in awhile. But yeah small things can change the whole outcome. I remember being stuck forever on an earlier level.
Heres a walkthrough you probably read..but whatever.
Infiltrate Kalinatek
You start up in a parking lot. Take out the two guards. Just wait for one to patrol the back area. Enter the office and get the Medical Kit. Pass through the door next to the office. Go up the stairs. Before you emerge from the door, let the 2 guards finished talking. When the guard on the left leaves, grab the guy on the right, drag him into the staircase and knock him out. Take out the next guards, which might be tough. If you’re spotted, go down the first staircase and break out your sniper. Zoom in with your scope near the office and you should be able to pick both of them off. When you’re done, climb through the opening on the right side of the wall. Jump to the set of hanging boxes and climb across the length of the crane’s arm. When you’ve fall to the next structure, turn around and jump to the building. Walk over to the small chimney and rappel the wall. Once you’re on the glass roof, go to the end and shoot a hole through one pane. Fall in. Kill the guard through the automatic doors and enter.
Disarm the bomb
Go through the office. When you find a dark room, enter the vent that is broken open. The narrow part on the right has a Medical Kit. It’s at the end on the wall. Enter the elevator. Stay in the elevator, creeping out of the opening slowly without emerging completely. When the lights come on and a fighting emerges, get back in the elevator. Snipe at the enemies from here. Continue down the hall and you’ll encounter two more guards. Without getting spotted, take these two out sniper style. Go into the burning room to the two hostages, but watch out for the wall mines. Approach the mines slowly and press A when the light blinks green. Run down the hall to the left and input the code 33575. Just before the fire, there’s a door on the right, which is trapped by mines. Run into the room quickly, just haul @$$ through all of the subsequent rooms since all of them are booby-trapped. When you get to the hall, you’ll encounter the Archives room, which is locked. Pick it and enter. Climb the file cabinet and defuse the bomb on the other side.
Restore power to the Fire Door Circuit
Leave the bomb room and head left. There will be two guards. Snipe the one at the base of the stairs from a distance. When the other guard emerges, quickly nail him too. Go behind the auditorium for a cut scene. Quickly set wall mines at the top of the stairs for a few easy kills. Back off a bit and open fire to get the rest of the scum. Go downstairs and get the items off of the table. Flip the switch on the wall.
Open the Fire Doors surrounding Ivan
When you come upstairs there will be a enemy in the upper seating. Snipe him before he can do any damage. Go up the staircase on the right and enter 1250 as your code. Kill the two enemies with your rifle who are in the room straight ahead on the second floor. Talk to the fallen NPC in the second room on the left. Pick him up and drop him at the infirmary. Kill the guard that comes to the infirmary entrance and talk to the fallen NPC again. Turn the corner and walk slowly past the enemy in the room on the left. Take him out with a headshot and check the computer to open the Fire Doors.
Find Ivan before the Russians and take his Encryption Key
Proceed through the opened door. Go up the stairs and open the door. Snipe the two enemies in the next room. Head into the bathroom and get into the vent. Kill the guard harassing Ivan. Talk to him. Leave him. Take the elevator up.
Go to extraction
There will be three guards ready to attack you when you’ve get off the elevator. Shoot them quickly. Go to the right side towards the guards; proceed to the last room. Get on the crates and get on top of the wall to the right. Once you’ve get to the other side, fall and proceed. You’ll encounter two more enemies. Kill them off quickly. The next room you’ll find three more guards. Go up a second set of stairs and turn left. Kill some more guards in a blue corridor. Turn the corner and you’ll see two doorways. Go in the second one and haul some arse. Some mines will soon explode. Kill another guard and you’ll be outside. Kill a few more guards and you’ll come to a cutscene. Now snipe the two enemies straight ahead and to the right of the opening. The three of them are in the red catwalks. When they’re dead, ascend the catwalks up to the chopper to complete the mission.