Unknown Command?

First, I am not a regular AutoCAD user. I regularly use another brand 3D modeling software. Basically, we only have a seat of AutoCAD (it is actually Mechanical Desktop 5 with ACAD 2000i included) to view customer drawings and do minor revisions. I have never had any formal training in AutoCAD. So please bare with my lack of intelligence.
On my first computer that I had when I started working here, I taught myself ACAD enough to where I could do basic things. I have since gotten a new computer and installed MD on it and set it up just as it was on my old computer. I have noticed that for some reason, there are several commands that give me an error of "Unknown command - Press F1 for help". I have used ALL of these commands when I used ACAD on my old computer. Some of these commands are:
properties find dwgprops 3dorbit adcenter etc.
Also with most (if not all) of my snaps which include: tt from endp mid int appint cen qua tan per par etc.
And also when I try to go to my: snap settings grid settings ortho settings polar settings osnap settings otrack settings but oddly enough I CAN get to my line weight settings
Does anyone know what might be going on here? If so, could you please explain the fix in simple terms. Remember I am not very ACAD knowledgeable.
Thank you,

How are you issuing commands? Toolbars? Menus? Keyboard?

I get the error regardless of how the commands are issued.

Sounds like serious problems with the install process: missing or incorrectly pathed .dll files or similar problems. Try uninstalling AutoCAD and reinstalling it. ___
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Type "Demandload" at the command prompt if the answer is 3 then it's a
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