Unfortunately, in February 2006, I injured my shoulders performing a set on the Hammer Strength chest press machine; I only had 25 lbs on each side, but after a few reps, I felt a "POP!" in my left shoulder. This injury occurred during the first few months of when I originally started working-out. The next day, I couldn't lift my left shoulder at all laterally (i.e., as if I was to flap my arms like a bird flaps its wings), although I could lift it directly in front of me (e.g., as if I was pointing to something in front of me). Ever since this incident, I have barely been able to (free-weight) bench press over 100-110 lbs without feeling intense burning and random clicks and pops in this shoulder. It's like the burning gets more and more unbearable with each successive repetition, where I have to go faster and faster until I just have to stop. My other (right) shoulder also experiences similar pain during pressing movements, though not as intensely as is felt by the left shoulder.
I guess I'm just trying to reach some sort of compromise: how can I build chest mass without further debilitating my shoulders?