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First of all you don't have to restore xoops, you have to restore working template. Depending on XOOPS version you have several choices.
In xoops2.2.x go to www.yoursite.com/recovery.php and set default theme to defaul.
On older XOOPS go to phpmyadmin and look for table xoospyounamed_config click browse, edit theme_set and under conf_value enter another theme name default should work in most cases.
Gediminas