Question: I am using Ubuntu 10.04 LTS, dual boot with Windows 7 on ThinkPad T400, I followed Ubuntu update hints and installed some update for my ATI Radeon graphic card, but when I boot to Ubuntu (means I can still load GRUB), the screen goes to blank and no matter what key stroke, I can not get any responds. I can't even open a terminal. 

However when I hit the power button, the computer would pop out the Ubuntu shutdown screen briefly and shut down.

I figure out I should delete the updates package for my graphic card, but I don't even get a chance to go to text terminal, please help me!

Answer: 
I got into the same "blank screen on startup" problem on my T400, after installing the suggested ATI driver. This notebook has 2 graphics chips, and the OS can switch / choose between them.
I could resolve the problem by adjusting two BIOS settings (hit F1 after power-on"):

1. Config > Display > Graphics Device: Discrete Graphics
2. Config > Display > OS Detection for Switchable Graphics: Disabled
ThinkPad T400 seems to be a laptop, but if you are using a different item just dismiss my answer.

What you are experiencing may be related to the ability of your video card to handle both the LCD and the external monitor configurations.

Even if this may sound silly, try connecting an external monitor and you may get the boot correctly in the secondary monitor. After that and just if it worked as we expect, upgrade or downgrade your video drivers in order to avoid this problem. My suggestion would be to remove all the drivers and after a reboot, try to install the one which was working before the update.