Theme in admin panel not showing

i have been having trouble linking from excerpts to the post. i get a old copy of my index page and instead of tabs with drop down menus i get a vertical list of menus. now i looked at my theme’s page in admin and the one i was using (in fact all) are not visible they have a broken icon where the image should be. i can’t locate the one i was using and liked when i do a search.
how can i resolve this issue. i’m new at this and would greatly appreciate some help. thank you for reading this. oh yes i tried to re activate but no go…nothing changed.