Why my GUI Image Labels wont show up using ClickDetector?

I made a GUI Image Label in StarterGUI > ScreenGUI. I made a brick in Workspace and added a "Click Detector" to it. To the "Click Detector" I added a script.. I typed this in the script:

script.Parent.MouseClick:connect(function()
	game.StarterGui.ScreenGui.EarthMonitorOff.Visible = true --Tried to find the Image Label
	wait(1)
	game.StarterGui.ScreenGui.EarthMonitorOff.Visible = false
	game.StarterGui.ScreenGui.MonitorBootUp:Play()
	wait(0.01)
	game.StarterGui.ScreenGui.EarthMonitorOn.Visible = true
end)

I made 3 Image Labels but not even one works and shows up. I am clicking the button and all I hear is the audio I added in line 5. Thats all. Can anyone help me solve this? I tried looking for an solution but couldn`d find one that would help me and fix the problem.

First of all, there would be no point in accessing the StarterGui as the GUI for the player is in the Whenever you want to do something GUI related, you have to do it in a LocalScript. So to do these GUI changes whenever you click the button, you will have to use a RemoteEvent.

First, put a RemoteEvent in ReplicatedStorage. Then, put a LocalScript inside inside of the ScreenGui.

Let's edit your server script inside of the part that you click.

script.Parent.MouseClick:Connect(function(player) -- connect is deprecated, player argument from mouseclick event
	local Event = game:GetService("ReplicatedStorage").RemoteEvent -- get RemoteEvent
	Event:FireClient(player) -- Fire the client
end)

Now in your LocalScript located inside the ScreenGui write the following code

local Event = game:GetService("ReplicatedStorage").RemoteEvent -- get RemoteEvent
Event.OnClientEvent:Connect(function() -- OnClientEvent Event fires when part is clicked
	script.Parent.EarthMonitorOff.Visible = true
	wait(1)
        script.Parent.EarthMonitorOff.Visible = false
        script.Parent.MonitorBootUp:Play()
        wait(0.01)
        script.Parent.EarthMonitorOn.Visible = true
end)

Now it should work.

Let me know if you have any more issues.

Since you have put the ImageLabel inside of StarterGui you need to locate the PlayersGui > ScreenGui because everything you have in StarterGui will be replicated inside every players PlayerGui folder. Also you should reference the PlayersGui with something like this using there get service function. Also please use a local script when dealing with player gui or the player mouse or anything that is client related that can be done on the users computer.

local playerGui = game:GetService('Players').LocalPlayer:WaitForChild('PlayerGui')

-- reference other objects needed
local screenGui = playerGui:WaitForChild('ScreenGui')
local imageOne = screenGui:WaitForChild('EarthMonitorOff')
local imageTwo = screenGui:WaitForChild('EarthMonitorOn')

-- then use your image references like this
imageOne.Visible = false

-- hope this helped now try to complete your script with the info i gave you :)

Note: For ClickDetectors you will need to handle the mouse click event on the server so you will need a script for the ClickDetectors mouse click event and use a remote event and use the FireClient function to execute the local script for the PlayerGui changes.