Can't login - site suddenly back to install mode

I restarted Firefox and suddenly my site is gone.

I made a new site with a fresh Drupal install a week ago, on a LAMP PHP 5 server with clean URLs. I've been working with my site off-line until it's finished.

After the Firefox restart, I can't log in anymore. I've tried the suggestions in the documentation and in the forum;
- using example.com/?q=user
- using example.com/user
- using example.com/?q=user/login
- using example.com/user/login
- using example.com/?q=admin
- using example.com/admin
- using example.com/?q=admin/settings
- using example.com/admin/settings
- I've cleaned out the cache and also tried Safari

The site only returns to the first install page what ever I do.

I've checked the database manually and the content I put in is still there. I've checked the site/settings.php and it seems OK. I worked with another Drupal site today and copied some stuff from this site, and perhaps I removed something.

To me, as a database rookie, it does seem like it can't access the database, but I've checked the settings.php and the settings are there.

Any idea of what to do?

/ Ayza