Tried everything but still can't UNROOT asus transformer prime

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http://forum.xda-developers.com – Ok my friend had rooted my Asus Transformer Prime TF201 and now have something called CyanogenMod9 on it. Well I don't like it rooted and wanted it off and back to stock. But when I tried unrooting it, nothing happen. I can't find my back ups files. I believe I try almost every method of unrooting it but no luck. I don't know if I'm doing something wrong or what but please help Can anyone suggest any ideas, I just want my Transformer Primer TF201 back to stock and the stock apps as if it was taken brand new out of the box. Please help and thank you. (HowTos)