[Koha] opac problem

im consistent on koha since few years back but on the librarian side, teaching koha users how to catalog, searching etc ... but not on the technical part especially on installation or error correction etc.....  It happened last month, when the technical people left the system with unfinished work.  he migrated to new version (version 8,x) in fact he did new/fresh installation from old version 2.2.9.  everything seem ok accept on opac part ... the opac page only show its work ! not as usual koha.  i m hoping someone here could lend some idea how to make it as what is opac supposed to be ? regards esmael