Is your FTP program set to transfer in ASCII format or Binary? I had the same thing happen last week. A lot of the nopCommerce config files are .txt and rely on newlines. If your FTP program is transferring them as ASCII it can mangle the newlines and the app can't connect to the DB so it assumes you want to reinstall.
This happened to me with Settings.txt and plugin description files.
This happened to me with Settings.txt and plugin description files.
You are right regarding the settings.txt file!!
nopCommerce is expecting \r\n, I had only \n, and kept getting the installation page.
I fixed that and now I get a different error:
Compiler Error Message: CS0104: 'TopicModel' is an ambiguous reference between 'Nop.Admin.Models.Topics.TopicModel' and 'Nop.Web.Models.Topics.TopicModel'
But that's a whole other topic!! So people, look out for line endings in your settings.txt file. Use Notepad++ :)