I would do this:
Remove all versions of AutoCad and remove all entries from the registry related to the application.
Create a system restore point.
Reboot the system
Reinstall the application and monitor for issues. When installing any other new hard ware or software during this period make a note of it and do a system restore point before any of them.
Now when the system goes haywire you know what is causing it.
And just a FYI if you are using a cracked version of AutoCad this is normal and I have seen it many times before if this is the case you will need to purchase the application for normal functions.