Canon 5D II Live View Problem

that happened to me with the 400 lens,it turned out to be the lens contacts, just worn and unusable, try covering the contacts with a small peace of insulation tape ,(the camera contacts) yo to focus and u will then have to use manual to focus the lens and camera controls . it was going to cost me 600 pounds for a service on the lens so now i use the tape and manual , in raw so dont loose a lot of control with the finished print
hope this helps
hope this helps