Why is my CSS media query being ignored or overridden?

Question

This is driving me insane! I've looked at a few questions on Stackoverflow and see that an ID element has priority over a class element (which is good to know but I have a feeling this isn't my problem). It's my NAVIGATION menu that I'm struggling with. (I use max-width btw)

Here is the GENERAL CSS for my NAV:

nav{ float:right; margin-left:2%;}
nav ul{ float:left; list-style:none; width:100%;}
nav ul li{ float:left; margin-left:5px; }
nav a{ display:inline-block; float:left; color:#f0f0f0; text-transform:uppercase; 
font-family:TrumpGothicWestRegular; font-size:1.5em; padding: 100px 20px 20px 20px; }

Now when the Viewport is UNDER 1140px, I want the CSS to change the menu like so:

nav ul li{ float:left;}
nav a{ float:left; display:inline-block; padding: 20px 20px 20px 20px;}

So basically the menu will float left with less top padding.

When the Viewport is UNDER 800px, I want the CSS to change the menu like so:

nav ul li{ float:none;}
nav a{ float:none; padding: 20px 20px 20px 20px;}

As you can see I've I only changed the NAV Float to NONE

Now when I test it, the GENERAL CSS works fine as well as when the view port under 1140px, but as soon as I go under 800px, the NAV still floats to the left!!?? It seems to be inheriting the CSS media query of 1140px? Any ideas?

UPDATE: This is how I am defining my media queries

<link rel="stylesheet" media="only screen and (max-width: 800px), only screen and 
(max-device-width: 800px)" href="small-device800.css" />
<link rel="stylesheet" media="only screen and (max-width: 1140px), only screen and 
(max-device-width: 1140px)" href="small-device1140.css" />  

Answer 1

Maybe there is something not right with your media queries? Try something like this:

@media all and (min-width: 1140px) {
    nav ul li { float:left; }
}

@media all and (max-width: 1139px) and (min-width: 800px) {
    nav ul li { float:left; }
}

@media all and (max-width: 799px) {
    nav ul li { }
}