What mod you wanna install ???
Manual installation or through NMM (Nexus Mod Manager) or Mod Organizer.
Nothing for both. I try install SKSE, and try install MODs direct by steam, only, i dont know need more things (i need it mod manager? if is is bad).
I only check in DATAFILES option and no see installed MODs and nothing work to MODs.
The say checking 1 of 10 (for sample) and stay in 1, and after seconds end check, i run normally but without mod.
To download a mod you will need to subscribe to it first. Have you done that ???
You can subscribe to a mod to it by selecting its thumbnail on the http://steamcommunity.com/sharedfiles/browse/?appid=72850.
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Why you don't download mods from Nexus instead ???
Just subscribe to nexus for free, and download any mod for free. (i thing it's much easier)
http://www.nexusmods.com/skyrim/?
http://wiki.tesnexus.com/index.php/How_to_download_mods
You can then install a mod manually, or if you prefer through NMM.
http://wiki.tesnexus.com/index.php/How_to_install_Skyrim_mods
Should i ask if you have moved your install folder to another location, or drive (HDD) ???
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Also can you check on that file:SkyrimPrefs.ini in the Documents\(User)\My Games\Skyrim folder if you have this: "bEnableFileSelection=1" ???
...and that's not read-only ???
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Make sure that the plugins.txt under C:\Users\[username]\AppData\Local\Skyrim\plugins.txt are writable by opening their properties and unchecking the "read only" check box.
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Also have you installed your mods in the correct folder ???
C:\Program Files (x86)\Steam\steamapps\common\skyrim\Data
Also, give Full Control permissions on your Skyrim folder