install ubuntu next to windows and no initial boot working

Hello,

I have installed UBUNTU from a CD following all the instructions among others on partition. It said at the end that it is installed and in order to use it I had to restart the computer. So that is what I did but then I have a message that it can not find information on C/S/ and no boot is starting and also no choice between Windows and Ubuntu. The only thing I have is:

grub rescue>

Can you help me in for instance the command I should give at that stage? It is a totally new computer and I wanted to use Linux and not Windows any more but do not know that much about Linux. I am for the moment working from my CD and it work but that is clearly not optimal.

Thanks for any help,
Denis