on the lock screen it says "Press and hold the power button, and than press the volume down button to unlock.
Are you sure that message was meant for only your Surface? E.g. on my Surface 2 Pro the equivalent of Ctrl+Alt+Delete involves the Power button and the Logo button. I know that the Surface 3 overloaded the use of the Volume buttons because it doesn't have a Logo button but I haven't seen a description of the buttons for your machine.
Another workaround would be using Narrator but getting it started on newer Surface models would run into the same problem: no Logo button and more overloading of the Volume buttons.
Also, I'm wondering if you can clarify what this procedure would imply on your machine, since it seems to suggest yet another way of overloading function via the Volume button but since my Surface 2 Pro Volume "button" is definitely a rocker switch I am very hesitant to try applying pressure at both ends of it the way this seems to imply should be possible:
<extract>
If you are in tablet mode, simultaneously press both the volume-up and volume-down buttons three times in quick succession (within two seconds).
</extract>
So, if you could press both at the same time that could make another possible combination with the Power button for simulating a Ctrl-Alt-Delete. I have seen a picture of it and it still looks like a rocker switch to me but perhaps you can press yours in the middle and get an actual button effect that way? Again, though I would definitely be hesitant to try applying force on both ends of a rocker switch.
HTH
Robert Aldwinckle