Ouch! That's what I was afraid you'd say regarding how you "added another site" to your DNN installation. Depending on how the hosting provider's DNN installer handled an installation over an existing site, you've basically done a failed upgrade from DNN 6.x to probably 7.1.x with the added problem that the site's web.config file was overwritten by that of the new install. Hence the reason that the install wizard appeared. My guess is that the database upgrade ran successfully before the install/upgrade failed.
At any rate, your best hope is to contact the hosting provider immediately to see if they have a backup of the installation's files AND database taken prior to your trying to add the second site. If so, it would be best to roll the site and database back to that from the backups. Most likely you will need help from the hosting provider to restore the database backup.
If the hosting provider does not have a backup of the site and database - and most likely they won't if it's been more than 2 or 3 days since the "upgrade" happened - we'll have to try to sort out exactly what has been broken and try to repair the site.
Here's some more questions and info needed if the hosting provider cannot restore from their backups:
1. Via FTP download the file dotnetnuke.dll from the site's /bin folder. On your local machine right click on the file, select "properties" from the context menu, and make note of the file and assembly version #.
2. Via FTP examine the site's /Providers/DataProviders/SqlDataProvider folder. Note the highest version number of the xx.xx.xx.SqlDataProvider files. Also look for xx.xx.xx.log.resources files. Any with xx.xx.xx greater than your DNN version # prior to the upgrade that are more than 1KB in size will contain errors logged during upgrade of the database.
3. Also via FTP look at the site's /Portals/_default/Logs folder for files that have names like InstallerLog#######.resources. Where ####### should be the date of the install/upgrade. These may contain other errors that were logged during the install/upgrade.
4. Do you happen to have a local backup of the site's web.config file that was made sometime (anytime!) before the problem occurred?
5. How critical is it to restore the site? Did it contain mostly text/html modules whose content can be recreated?