Start up boot camp problem

[Nordichund]

I don't know what has happened but I cannot get into Boot Camp by holding down the alt key upon restart. I have to go in to the start disk and click on what is now an image of a Windows folder. The image of the hard drive has completely disappeared, but the image that is on my screen is still there, but it dissapeared for a while earlier today and did not return until I performed a restart.

If I do restart into Boot Camp using the start up disc way it works perfectly.

Any ideas of how to bring back booting into Boot Camp by holding down the alt key?

Thanks for your time.