Did you at some point run the program "Mirage"? If so (since that is the only program I know that turns the dock transparent and works great in 2D) then you need to check out how to undo it from that program. It is simple to undo, but I just don't remember at the moment how you do that- I think you just rerun it and tell it to restore the original dock, but I'm old and probably just imagined that! 😉
On the other hand if you didn't run Mirage at some point all bets are off- and you can just use one of the free SuperDocker type programs to install a new dock of your choice which will take the place of the transparent dock.
