Use the strength of your community to help rebuild your site. You might have lost your member list, but your members will still know other members.
You need to get your software back first, someone somewhere must have a copy. Email attachments, usb drives, etc.
Then set the members who have contacted you a challenge "Can we rebuild it bigger and better than before" and emphasise the WE.
Off the top of my head here, but how about making it a competition. Who can contact the most other original members and get them to re-join and upload their stuff.
Thinking about the branches of a tree, could you create something to graphically link and display all the new joiners so they can see the progress that is being made. Person A contacted Person B who contacted Person C, D & E etc.
If the community you have built is half as strong as the one here (and this thread is testament to that) you will have your site back up and running in no time.