If I'm understanding your post, your OST is set to offline mode, and you cannot seem to log into the site to turn it back on?
If you goto http://yoursite.ext/scp(http://yoursite.ext/scp) and log in you should be able to turn it on in the admin panel. If you cannot get to that you might need to re-upload the source in /scp to your host.
Alternatively you can manually edit the config in MySQL to make it online. To do this you would get to a mysql> prompt or utilize a web gui to edit the ost_config table directly and change isonline to 1.
Alternatively you can run the following MySQL query:
UPDATE ost_config SET isonline='1';
If you used a custom prefix_ change the code above to reflect the prefix you use.
Let us know how you make out.