Ok, I might be wrong about having to install lower PHP/MySQL versions to begin working. Just installed a 1.7.7 via git and it functions ... there are depreciation errors/warnings, but none that I've found that would cause things to fail. PHP 5.3.3/MySQL 5.5.37
Been thinkering ...
Wonder if accounts in the DB for your M17 have all been set to 'disabled'?
(I don't re-call what version of Moodle began that). The accounts are there, but the data has been changed in such a fashion to render it's usage useless. Only the original admin account might NOT be affected.
What does command line query of the DB for the moodle and the mdl_user table show for the login name you are attempting to use?
ie ... what does this query show:
mysql> select username,password from mdl_user;
In the mdl_config table for a 1.7.7 version, there is a variable
longtimenosee set to 120 by default.
select * from `mdl_config` where `name` like "%longtime%"
That's 120 days. Could be that all accounts have undergone a change.
Earlier versions of Moodle used MD5 for password hashing - no salt. Salt was added with version 1.9.6 (if I re-call correctly).
The same query above will show the password for username as an MD5.
Might be able to use http://md5.gromweb.com/
to convert the md5 string seen for the password into humanly readable.
**OR** one could use the site to create a known password and get it's MD5 equivalent.
Then use whatever tool you have to change the password to the now known MD5 equivalent.
(if you attempt this save the original data for the password field to a text file on local system to change it back if this idea doesn't work).
'spirit of sharing', Ken