I'm a level 14 assassin/thief and I am unable to backstab. I have enough sneak to sneak up behind the first and kill them in one hit. I have trained the backstab multiplier. I have tried using all daggers along with trying 1 dagger at a time and dual wield. I sneak up behind them and hold down the attack button. This just displays an animation of a really strong dagger strike and they die. There is no actual backstab cut scene type animation. Am I doing something wrong?

The animation doesn't always play (unless you use a command to force it to always play).

Try not power attacking.

You also need to be very close to them.

Make sure you are not detected. Your cursor should look like this. ---:---

It works almost 100% if the time for me.

Btw no sneak finishers for most critters unless they are humanoid like dremora, Draugr and such. Trolls and the like I seem to get few finishers of any kind on. Even regular ones.

For fun.. http://cloud.steampowered.com/ugc/648747634048117624/8C164B541D4ACCD0499687C541320F31BE91C2BB/
http://cloud.steampowered.com/ugc/648747634048118709/1C9A4996F22310A80CAE202C32F1EDD8D3BDE0F8/

Its easy you don't deal enough damage to kill them with one hit in sneak, thats why you don't get the kill animation, take som perks that makes you deal more damage and it should work. If not I don't know :S

Probaly not mate =) In my experience there are some instances where the backstab animation simply wont work for whatever reason. It doesn't work *all* the time and can be pretty random sometimes. So,dont worry id say,its not broken. Go somewhere else and youll find it works fine =)

It won't work from power attacks. It has to be a normal swing.

Pretty sure thats not true. I figured that the rule that governs if you get a kill animation or not depends on the mob your dealing with and how powerful it is compared to your level. If its some low level bandit then you will get a kill animation from a normal swing,where as if its a chief or something higer level,a normal swing wont automatically one shot them..most likely youll chip their health a bit and a fight will start (unless your quick about getting a second stab in). However,if you power attack that same higher level enemy,youll get the one shot kill animation. Thats my experience of it anyways.

You have to sneak and hold R1, at least on PS3.

Nubius is correct.
Normal attack only. A power attack starts a brawl or sometimes an instant kill shot without the cut scene.
I'm on the 360 and I get the throat slit cut scene every time... And I absolutely love it.

I think the one handed sword perk with critical increases the chances of the animation.

Thank you

You can get the animation whether you power attack or swing normally. It seems completely random to me.