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
You could try booting into safe mode if GRUB loads correctly and fixing the driver then by choosing System-> Administation-> Additional Drivers and use the ATI proprietary driver. 

Once done you will need to reboot and you should be into a normal desktop.