I am using a Mac and had an existing installation of WP using MySQL for database. I backed up my database to a .sql file and installed MAMP, which overwrote a lot of settings on MySQL. I am able to recreate the database by importing the .sql file, and still have my WordPress installation, but when I try to log in, I get referred to an installation page which gives me an error. Again, I have my database and I have all my original blog files but my MySQL and Apache (root directory) have changed and I can no longer access my blog. (I am aware of the string serialization problem and have used the searchreplacedb2.php to modify the paths to my new Apache root directory, to no avail.)
Thanks a lot!