Win 7 won't boot with BC - but will in Parallels 7

I recently ran a Windows Update on my partition, and after shutting down (let the updates complete after shut down), it no longer boots. I hold the option key, select Windows then just get a black screen and a flashing '_' for about 5 seconds, before restarting again and booting into OS X.

At first I thought Windows 7 might have corrupted, but I can access it fine through Parallels. I've Shut Down Windows in Parallels so that shouldn't be an issue.

Any ideas? I'm runningthe latest versions of Windows 7 and 10.8 Mountain Lion on a 2012 13" Macbook Pro.

Thanks 🙂