If you are having problems with your shout not unlocking even though the shout tab shows you have dragon souls available try this:

Save your game BEFORE you do this.

Go to the shouts tab in the magic menu.

Cursor over a shout you need to unlock yet so that it is highlighted and the description box appears.

press each letter key one after another to see if the unlock 'R' key is attached to another letter key.
(I found my unlock was attached to my A key which I use to equip and unepuip my weapons.)

If you go through all the lettered keys without the "Spend Soul" box appearing then try the specialty keys ie. ( [ \ / . ; control, alt , tab etc.

One of the letter or number keys WILL unlock the shout it's just a matter of finding out which key it is.

Or you know, you could just see what you have bound the equip/unequip spell/weapon button to? :X

Yes you could IF you know your way around the game files, if you don't or are a novice this is the simple solution.

Uhm...

Options menu, controls... Its in there with the rest of your keybindings