Thank you for your post.
FileMaker Pro 10 will NOT deactivate any previous version of FileMaker Pro. Something else has occurred.
What occurs when you launch FileMaker Pro 6? Do you get an error message? Any other information you can provide may be helpful in narrowing down the possible cause.
On a side note, this is a public forum, and we do not recommend posting of personal information as anyone can come here and scrape information. You may want to consider editing your post and removing the personal information.