Screen display problem LINUX Mandrake7.1

Hi
My Name is Melt from South Africa.
Today I installed Linux Mandrake 7.1 on my computer to see how it works, but I am an empty shell with Linux. After installation when I want to run the operating system, all boots fine until the point where I suppose I would see the screen.
Here my display goes skew like the resolution is wrong. I thing I must have chosen the wrong screen during set-up and now I do not know how to fix it. Can any one advise me please?

Thanks
Melt