You might have to uninstall the current version of autocad you have on your computer then restart your computer then run the jet clean utility. http://download.cnet.com/jetclean/3000-18512_4-75627788.html
JetClean tidies your registry, gets rid of junk files, deletes broken shortcuts, and attempts to give your computer that like-new feel again. Then delete cookies Here is a very simple guide on how to delete cookies manually from your computer.
Click on "tools" in your browser. This is usually located in the upper right corner of your browser. Click on Internet options. This will appear in the drop down box and is usually at the bottom. Under the "General" tab look for "Browsing History." Under this heading you can click "Delete" to have the computer delete all cookies for you automatically however to delete the cookies manually click on the "Settings" tab Click on the "View Files" tab under the "Temporary Internet Files and History Settings" box that pops up. When you do a second box will pop up with a list of cookie containing files. This may take a few seconds to load so be patient while waiting for the cookie files to load. Highlight any cookie file that you would like to delete. You can highlight more than one at a time by holding down the 'Ctrl" button on your keypad Delete the files that are highlighted by clicking on the "delete this item" located to the left in the same box. As soon as you do you will see the selected files disappear. When you are done just "X" off; this completes your task of manually deleting cookies. You might also do a disk clean up click start click on computer to open right click on your hard drive usually C: select properties in the general tab select disk clean up click ok you can view files to be deleted. Then reinstall it
Hope this helps.