As usual, Dave has the answer. This happens a lot to students in my classes, they inadvertently make components inside other components, sometimes a complete copy of a component on top of the original. Be careful when you click and double-click. The first click will select a component or group so you can move it. If you double-click instead (easy to do if you're getting frustrated) you open it up for editing.
Look for the visual clues that will tell you what you're working on, and if you're inside a component or group. The rest of the model will dim if it's open for editing. You can also select an object and the Entity Info window will tell you what it is. It also pays to pay attention to what becomes highlighted when you select, if the whole cabinet is highlighted when you click on a part of it, that means you have combined it somewhere along the line into a group or component.
The explode command will take a group or a component apart one step at a time. If it's nested (made up of other groups or components) the first click with explode will reduce it to those sub-groups or sub-components. If you keep exercising the explode command, you will eventually get down to edges and faces and a sticky mess to deal with.
A common scenario I see is this: you want to move a component, but you're a little jittery and double-click. Instead of selecting it, you've opened it to edit, and when you move something, all the other instances of that component change. Even worse is if you let your finger hit the CTRL key and you make a copy when all you wanted to do was to move the thing. Then you realize that isn't what you want to do, and click again instead of hitting the ESC key. Now you have a copy you don't want inside a component that wouldn't move.
SketchUp can be quick, but as you're learning the best thing you can do is slow way down and be sure of what you're doing before you click.
hope this helps,
Bob Lang
Bob Lang