I have a Canon 1000D (Rebel/Kiss) which came with an EF-S 18-55mm f/3.5-5.6 IS lens. The set is about 8 years old now. Lately the auto focus has been playing up. After one shot, it stops working. When I attempt a second shot, no red auto focus dots appear and there is no beep. The green focus lock light appears in the viewfinder, but the shutter will not fire. If I switch to manual focus, wind the focus dial all the way out, then switch to auto focus again, I can take another shot with auto focus before it stops working again. I've tried resetting the camera and cleaning the contacts on the camera and lens. When I put a friend's lens on my camera, auto focus works properly. I've also opened up the lens, pulled out all the electric wire ribbons and reinserted them, to no avail. Any ideas?