If it can find the folder when you are logged in as Administrator, I would look at increasing your user level to a minimum of Power-User (as recommended by Autodesk).
You could have a problem with your User Profile on the system (may need to recreate), but I would look at sercurity levels first.
Ok, but how to go to registry ,and in which folder can i make this change? I have Libre office, should i turn it into ms office?
This thread concerns OpenOffice and Inventor. The Word Document posted in this thread explains how to go about editing the Windows Registry.
Never heard of Libre Office before, I have no idea how it interfaces. Best suggestion would be to install OpenOffice, you might be able to use the current version of OpenOffice without having to edit the Windows Registry.
Start with some of our most frequented solutions or visit the Installation and Licensing Forum to get help installing your software.