About windows installing

Hello,
My problem is I have two drive one is 40 GB and one is 80 GB I have installed window xp on 80 GB hard disk I was try to install win 7 on my 40 GB hard disk but I forget to format the the c portion and I installed the window 7 in my 40 GB when I start the process of installing window it start coping then the window 7 logo came means the windows logo came then suddenly a message occurred that your system has been shut down when I power on my computer it keeps doing that