So I was in this cave in Skyrim near the mountains and I was right about to kill this bandit thug (basically boss battle for that area). Right as I used my "relentless force" absolutely nothing happened. I kept pressing the button and nothing happened, so I checked if I had it on. It said I had 0 shouts left, which confused me. Why do they run out? How do you fix it? I can't kill any dragons because I'm a low level so if that's how you fix it I'm screwed.

Eh? They shouldn't run out, only need to recharge...

I'd like to know as well.

The zero left is how many new ones you can learn. When you kill a dragon that will go up by one. There is a cool down on shouts. You can tell how long the cool down is by the blue color on your compas bar

Yeah but that bar was completely full. I hadn't used a shout for awhile, so it was full.

Don't take this the wrong way - are you sure it was equipped? Sometimes my Beastform power magically vanishes from being keyed up (possibly a glitch), maybe that happened here?