The screen looks like it’s on drugs

This problem is known colloquially as, “The screen is all messed up” or “My computer monitor is possessed.”
 
The psychedelic screen issue manifests itself in many ways, but the root cause is almost always a connection problem between the VGA cable and the VGA ports. 

When the VGA cable comes slightly loose, it causes the screen to glitch out in all kinds of wonderfully random colors, or display similarly spooky behavior. For this, the fix is so simple you don’t even need to be called out. 

If you are already on-site, you can always make a show of the solution so it sticks in the affected end users’ minds, allowing them to fix it themselves in future. Crack your knuckles and tell the end user to step back. Now, carefully wiggle the VGA connector and then slot it firmly back in the port. Ta da!