So I went to Valthume in search of a word of power but when I located it I wasn't able get the word!

Same thing is happening to me at Lost Tongue Overlook. Killed an Elder Dragon, I can hear the chanting and sizzling but no word. I've been back twice to see if it has appeared but so far nothing has changed.

That happened to me for 3 words during my first play through on the PS3, so it seems to be a common bug.