A screenshot would be a good improvment to your post because i am not sure that a lot of people already have experienced what you are describing.
Recover your file is a good idea, just to see. More info are available here : http://www.filemaker.com/help/html/recover.39.10.html
A little comment, more consideration than troubleshoot suggestion : you are creating new databases that take time and moreover, your are learning "the new way to do" introduced many years ago with 7 version. Why don't you use directly the last 12 version instead of learning techniques that may be already "has been" ? Note that you could first try to install the trial version (no bad effects on your existing FileMaker Pro 10 installation). No offense to you, just sincerly trying to help... The link : http://info.filemaker.com/US-en-FMP-Trial-Form.html?try=fmp12-product-try
Edit : Also this link would help to convert your fp7 files to fmp12 format : http://help.filemaker.com/app/answers/detail/a_id/10571/kw/converting