Windows Startup Problems in Bootcamp - 2013 iMac

I installed windows 7 via bootcamp and all seemed to work out well.

But then I downloaded and installed the windows updates and this forced my iMac to restart a few times.

It seems like sparatically on restart it either boots right into windows or before windows starts to load it gets hung up on a white/grey screen. (the iMac is still defaulted to startup windows I haven't changed that yet)

So in the latter scenario I have to hold the power button down to shut off the iMac and then restart and then it loads windows properly.

Is this a common problem or does it sound like something might be wrong?

Maybe something with my bootcamp is wrong?

This is my first imac so maybe it's a common thing?

Any help is very much appreciated.

Thanks.