Nice models and images. I like especially the first one, Icegrip

I nearly used Free TG2 for 2 years and had not such a problem.
Curious what you did...
Look here:
http://www.planetside.co.uk/content/view/21/36/
"The free version may only be used for non-commercial purposes and is limited in the following ways:
Render Size Maximum: 800x600
Render Detail Maximum: 1.0
Antialiasing Maximum: 3
Maximum Number of Rendered Populations: 3
Maximum Render Detail for Micropolygon Export: 0.1"I am not sure that this was your problem , you do not look like a beginner at all , but anyway...
Look at the upper left side on the menu bar in TG2. "File" then "Save as" .
Or directly use this key combination "Ctrl+Shift+S".
Write anything you want for your project file name .
Your project file will have a TGD extension . Thats it Icegrip.
Sad that you loosed th project files . I liked them.
I think you will make better ones easily
Edit: Search your hard disk for files with the "tgd_bak" extension.
If there are any, change the extension of them to TGD (be careful and give them other names) and try to open them in TG2 .