Liquify Tool is having no effect

Hi,

I have opened the liquify tool in CS6 for the first time. All other tools work however when I click on the liquify tool and it opens its separate window, clicking on the image has no effect and it literally remains unchanged, not a pixel moves out of place. One thing to note though is that when I do click and drag around the image, the "restore all" box becomes active which surely must indicate that CS6 is assuming a change has been made hence it will restore it to how it was before? Even though a change hasn't been made. I have attempted to change performance options of using/not using my graphics card. I have played around with the layers but still no effect. I have changed the brush size and also clicked on the advanced options and clicked "show backdrop" after which I played around with the mode but still no effect. All the changes I made to rectify the issue were from other forum posts (all of which remained unsolved) but still no effect.

If someone can help me with this it'd really be helpful as it's very frustrating to not be able to use it.

Thanks