TheSilencer, you're thinking of level 6.
Kiran, this is late, and you probably figured it out yourself; at level 8, in that last screen, you have to ignore everything else and get to the defense gun computer. Only shoot enemies if they block your path. Don't shoot cameras. Rely on obstacles to block turrets. Just use medkits and energy cubes to keep yourself alive and get to that terminal. A few switches will have to be thrown, but other than that you're pretty much just running there. Once you switch it on, then you can kill everything in sight.