Bootcamp Stuck on 'Please Press Any Key to Boot from CD or DVD'

Hi,

I've been trying to run WIndows 7 on my 10.8.2 Macbook pro, but keep having issues. Yesterday, it seemed like I had figured it out, but it got stuck on the 'Expanding Windows Files' step, so I cancelled the installation. Now, I can't even get back to that step. Whenever I try to get onto my windows partition it says 'Please Press Any Key to Boot from CD or DVD', and I can't get past it; pressing keys doesn't do anything.

Thanks