Can't install Windows 7

I've got my install disk, I've portioned through bootcamp and the Mac restarts and boots from disk. It takes me through the Windows Startup Manager with which I select Enter Windows Setup.
A bar loads and says Loading Windows Files and it then displays the four coloured symbols and they sit there pulsating.
That's as far as it gets. I've let it sit there but nothing happens. I've installed windows before this exact same way, but I needed a larger disk space.
Any ideas how I can remedy this situation?
I'm using the 2011 21.5" i5 iMac

 

But I haven't changed anything from when I removed the partition to when I made a larger one. It worked flawlessly before, but I can't find anything on this issue anywhere.