So if immediately after the server reinstall, Moodle stopped working, then that is probably the cause. If Moodle worked for a while after the reinstall, then it may not be related.
If that is the cause, and without knowing why a reinstall was necessary... Have you double-checked your config.php to make sure that the settings are correct, especially database and moodledata. Is it possible that moodledata was corrupted somehow? in the process of reinstalling?
Something to try... run this from the moodle site directory:
I don't know the insides of Moodle well enough to know what might trigger that error. I do copy Moodle sites often enough that I know moving it between servers works fine when you follow the migration documentation, and certainly, if you backed up the site php files, moodledata and the database and restored them properly to a reinstalled server, that should work fine.