problem with installing ubuntu using windows installer - black screen

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http://askubuntu.com – I installed Ubuntu using WUBI, windows installer. It asked me to boot and while booting, it offered me to start using Ubuntu. I chose Ubuntu and a screen came saying I can go to options menu using Esc, if I entered Esc, it asks me which mode I'd like. I entered demo mode. It then froze for a while with a black screen before shutting down automatically. I then restarted again and didn't enter Esc. It took me to a black screen again. Which key would get me to grub so I can enter my system again. I have a 1 GB nVidia graphics card. (HowTos)