I agree with Chris. If you provide how far can you go in the booting we may be able to help you.
Here a couple of pointer to a very useful CD that will allow you to format and do many other disk jobs.
Rescue CD contains gparted the second is gpart alone what makes it a little simple to use.
They work very well.
If you have valuable data you most likely can copy it before formatting. For that you can use any of the live CD, my preference goes to one of the small distros dsl-n that you can run from a cd or like myself from a small pen drive (>100 MG). Then you can mount the partition that you are going to format and copy or burn it to an optical medium.
There is a dsl-n forum here.