Ok if you have them installed you will need to activate them from the launcher that starts before you get into the game. You can do this by clicking on the data files in the launcher pannel then check to see if they are marked with the little tick. If not just click on the boxes then click on ok then click play on the launcher pannel and that should be you.
If they still do not load up then your dlc's are corrupt and you will have to varifie your files by going to your games library and right clicking on the Skyrim name on the left click properties then click on the local files tab in the little window that has come up. Then click on the Verify Integrity of game cache.
first the data files on launcher didnt work,then i copied this:[Launcher] bEnableFileSelection=1 in skyrimprefs.ini in Skyrim folder of my documents and data file on launcher worked and the DLCs loaded,the strange thing is that my cousin didnt these things but they loaded for him,anyway thanks.
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