Reset your AutoCAD Windows Profile
Have you even run into a problem in AutoCAD (or a vertical such as Civil 3D), that you can't figure out such as a drawing behaving strange, commands not acting right, commands not working, or maybe even the whole application just won't launch? One of the first things I would suggest is to have someone new log onto your machine and launch AutoCAD under their Windows profile, essentially creating a new "AutoCAD Windows Profile". If the problem goes away when you do this, then it is probably some error or corruption in your own "AutoCAD Windows Profile".
In most cases, it will take more time to track down and fix the problem than it will to just start fresh with a new "AutoCAD Windows Profile". How can you wipe this out, without wiping out your entire Windows profile? Click here and follow this excellent step-by-step process. When you are done and launch AutoCAD, your "AutoCAD Windows Profile" will be reconstructed from scratch, just like the first time you ever launched it.
Note that this is different than running a repair (initiated from Control Panel>Programs). A repair fixes program files, while reconstructing your "AutoCAD Windows Profile" affects your user files. Find more detail on this process at the link above.