Mac cannot boot

Hi, I'm currently using the latest mac with snow leopard OS. I initially used bootcamp to install windows xp. However, with the upcoming windows 7, I wanted to remove xp and reinstall with windows 7 instead.

However, I couldn't manage to boot the computer from the windows 7 dvd. As such, I used the Mac OS's bootcamp assistant the remove the former partition for windows xp. Then, I re-setup the partition again for windows and restarted the mac so as to install windows 7.

However, after the chiming sound, and after the white page, the page came into a blank (black/white) page with a flashing "-" dash sign at the top left hand corner of the page. It stayed there for a long time.

I then restarted the computer and the same thing happened. I tried using my wireless keyboard to press the option button to load in mac os but nothing happened.

Will really appreciate any help as I can't load anything to solve the problem at all...

Oh, and I can;t load any disc in as there's another disc inside and I couldn't eject it...