Help with if/else ParticleEmitter Script?

On line 4, you're defining pe with multiple values. This is what arrays are for. Essentially, lines 9 and 13 are only affecting the first value assigned to the variable. Here's an example of how this works:

local blah = "1",2;
print(blah) --> 1 (only "1" is assigned to 'blah')
local first,second = "1",2;
print(first,second) --> 1 2 (a reference was made for both values)

You can take advantage of arrays here. Put all of the Particles in an array, then iterate through the array and change each index's Properties.

local nob = script.Parent.HeadandNob.Nob
local head = script.Parent.HeadandNob.HEad --Typo?
local pe = {head.one, head.two, head.three, head.four, head.five, head.six. head.seven. head.eight. head.nine, head.ten, head.eleven, head.twelve, head.thirteen, head.fourteen, head.fifteen, head.sixteen, head.eighteen, head.nineteen, head.twenty, head.twentyone, head.twentytwo, head.twentythree, head.twentyfour} --Array
local state = script.Parent.Value

function changeStateTo(bool) --Parameter: true_or_false.
    state.Value = bool;
    for _,v in next,pe do
        v.Enabled = bool;
        wait();
    end
end

function shower()
    if not state.Value then
        changeStateTo(false);
    else
        changeStateTo(true);
    end
end

--`connect` is deprecated.
script.Parent.HeadandNob.Nob.ClickDetector.MouseClick:Connect(shower)