AFTER PICKING UP SAM, THERE IS NO NEW EXIT AS THERE IS SUPPOSED TO BE. DOES ANYONE KNOWS A SOLUTION? IT'S PITCH DARK, I CAN'T SEE WERE TO WALK.

HAHA, your lucky i decided to play through SP finally.  i actually did this level last night.  

right when you walk in the room where sam is lying, you pick up a socom.  it has no bullets in it, but you don't need bullets, you need LIGHT, and it comes with a flashlight equipped (how convenient).  so, pick it up, hit "[" to turn on the light.  

after you talk to sam, there is another explosion, and the opening at the end of that room opens up.  go through there, drop down, find the valve to turn off (BTW, i ran into a bug here, if you have the socom out, and roll the mouse wheel forwards, it will put it away, and you will NOT be able to turn the valve for some strange reason).  so, the valve kills the steam, now you can pick up sam, and make your way outside.  

make sure you haul sam all the way to the ambulance, or the level won't end.

How do you pick up sam's body and how do you drop it???
Can someone help me,plz?

If I remember correctly, you go over to him and press the "Use" key.