Hi
In the video you linked to, the guy shows a very normal noisy signal. It has noise on the display and the same noise causes the trigger to move things around. It could be from:
1) Bad scope probe
2) Bad probe ground
3) Ground loop between scope and signal source
4) Bad BNC on front of scope
5) Bad input amp on scope
4) Bad sampler in scope
5) Bad sample clock in scope
6) Bad power supply in scope
7) Bad connector from scope power to main board
Bad ground on main board to case
9) Bad ground from power supply to case
10) Bad filter on power supply to AC line
11) Bad ground on scope to AC line
12) Wrong trigger setting
That's the short list of things to check out. Depending on what you find, there is a longer sub list under each of those.
Bob