This issue has now appeared on 3 T420s units in the past 2 months.
The user will be working along without any issues and then just like if someone pulled the antenna cable out of your TV set the screen will go to complete static.
This is not an LCD issue as the static appears on both the internal LCD as well as an external monitor.
It appears to be a video card issue as repalcing the system board has resolved the problem.
Has anyone else experienced this issue?