I've just went back in the embassy via top floor, dropped through a vent shaft, and i'm stuck. can't open main doors/jammed other door has keypad but can't access. What gives?

Not sure which console you're on, and I'm assuming from the description that you're on the second Chinese Embassy mission.

Once you drop down move forward until you reach a room with a medkit. Look to the right and you'll find an area with broken boards and light coming through them. Stand and use the 'back to the wall' move so you can squeeze through a small gap. Move to the end, jump to the pole and slide down. You'll have to use the BTTW move again to reach the next challenge - a room with 3/4 gun happy guards! Enjoy!

i think he is passing by the guys destroying computors then the next key pad you need to use your thermal goggles

Since he noted that he just dropped through a vent it's more likely he's where I suggested.

I would think that if he were at the keypad door (in the hallway upstairs after the 3 gun happy guards, 2 more guards where a camera is and then 2 sleeping guards) he might have mentioned the sleeping guards?

hi,iam on xbox my ? is how do i get in to the embassy? Thank you for all the help.

Okay, assuming SC1 (stealth action redefined) there are two Chinese Embassy missions:

1. Chinese Embassy I

Ignore your handler, turn around and head for the alley just ahead to your right. Jump onto the dumpster, then over the wall. Run full speed down the next alley until you're close to the end and do a 'drop-roll' so that you come out of it close to the exit. Crouch walk to the left (behind the stand) as close to the wall as possible, then as you clear the stand move past the barrel keeping as far left as possible (this blocks the two guards from seeing you. Once past it, stand and run full speed past the 'fire barrel' ahead then right towards the dark corner where you'll find a ladder. Need more help after this, ask?

2. Chinese Embassy II

Move towards the red lit restaurant doors and enter. Crouch walk against the right wall past the barrier then turn left and sneak through the tables to the kitchen door. Wait there until you see the chef turn away from the cutting board. Enter and sneak left until you reach a ladder. Climb it, then a second ladder. Cross the planks there and put your 'back to the wall' while standing and wait for the patrolling guard to head past you. Crouch walk through the room to the other side, out the door to the right and find a zipline. Need more help, ask?