HL2

hi, im in the section called "follow freeman", anyone not at this point in the game don't read on because it'll spoil it. barny has opened some door for me and is telling me we've gotta shut down a big weapon thats stopping us from getting through the gates of the tower. only problem is i go outside and get killed, the only way i can see is to go backwards, cos outside all the paths are blocked. he keeps saying follow me but does f**k-all. can anyone give me a pointer?

keep running strait.. at the end there'll be a building on your left with a door.. ats at the end of the fence.. (with that musem type place right? and the artillary?)