What version of the game are you using?(out-of-the-box, v1,1x, v1.20416?) Oblivion patches;
http://www.elderscrolls.com/downloads/updates_patches.htm )
Also, check that your folder setup inside Data-folder is EXACTLY like I'm showing below this paragraph a bit later. When checking your folder setups, make sure it's 100% identical to what it was in the .rar/.7-zip/.ace file, while following the below mentioned format.(Eg. possible subfolders for textures etc. But under no circumstances should there ever be a duplicate of the parenting folder, eg. Data\Data\, Textures\Textures\, you catch the drift.):
X:\xxxx\Bethesda Softworks\Oblivion\Data --> All esps here.
X:\xxxx\Bethesda Softworks\Oblivion\Data\Textures --> Folders containing .dds and _n.dds files go here.
X:\xxxx\Bethesda Softworks\Oblivion\Data\Meshes --> Folders containing .nif files go here.
X:\xxxx\Bethesda Softworks\Oblivion\Data\Sound --> Folders containing any sound(.wav, .wma etc.) or .LIP files go here.
X:\xxxx\Bethesda Softworks\Oblivion\Data\Music --> Folders containing any music files go here.
X:\xxxx\Bethesda Softworks\Oblivion\Data\Video --> .bik files go here, these are pretty much the animations in the game.
X:\xxxx\Bethesda Softworks\Oblivion\Data\Shaders --> .FX files and .SDP(Session Description Protocol.) files go here. No mods should edit these.
X:\xxxx\Bethesda Softworks\Oblivion\Data\DistantLOD --> .lod files go here.
_________________________________________________________________
X:\xxxx\Bethesda Softworks\Oblivion\Data\obse(Created by Oblivion Script Extender)
X:\xxxx\Bethesda Softworks\Oblivion\Data\Bash(Created by WryeBash)
X:\xxxx\Bethesda Softworks\Oblivion\Data\Bash Patches(Created by WryeBash)
X:\xxxx\Bethesda Softworks\Oblivion\Data\Docs(Created by WryeBash)
X:\xxxx\Bethesda Softworks\Oblivion\Data\INI Tweaks(Can't remember.

)
X:\xxxx\Bethesda Softworks\Oblivion\Data\LSData(Can't remember.

)
X:\xxxx\Bethesda Softworks\Oblivion\Data\menus(Any HUD/UI changing mods.)
If your folder structures are correct and all the files are where they belong, your game most likely isn't patched to the newest version.(The link is at the top of this post.) The fact that the esps don't show in the data files selection would point that the .esp file isn't in the correct directory/your game isn't patched up to the newest version. The fact that an activated .esp doesn't make a difference in-game gives a 99% probability that your game isn't patched to the corresponding version/newer one. When you are patching your game, make sure that the patch is the right one for your game version/region/language.
~Elraine