Here's the latest for any very welcome detectives...
Alternatively emptied the database and imported either the backup file with the data, or the default info (and data). The uploads each presented a working blog. Only difference is that with the default data everything works; with the real backup data it generates a blank screen at a login attempt.
The new install is 1.2.2; and I'm almost certain the old one was too - if not it was 1.2.1. The data was converted through a separate 1-click backup from 1.02blakley when I upgraded to 1.2.x.
I've been through the posts for blank screens; this problem seems different:
--If I click the refresh after the blank screen, I get a login dialog.
--If I fill in any of the known user/pw sets, I get a 'session expired' mssg.
--Permissions are set to 755 folders / 644 all files - just as uploaded from the zip file. If I raise the wp-login.php to even 664, I get a 500 error, and the error log says the file is is allowing others to write to it.
In phpmyadmin, the site_url looks fine; wasn't sure if the options on the original install were set with the blog pointing to the root, but I don't know how else the blogfilename says '../index.php' instead of just 'index.php' then, but I tried changing it to the latter anyway - no go. (I can't get into the admin to change or even see the settings from there - wasn't sure I read it right in the files).
--I did notice an error in the logs, but not sure with which version it occured or how:
'Premature end of script headers: /home/found/public_html/wp-fdn/wp-login.php'.
It seems like a hot lead since the login is the file that seems to be choking. I looked at it though and everything seems in order, even down in the config.php file that is a require file there.
this is as far as I gotten.
i hope someone can help soon; the walls are starting to look climbable.