Bootcamp unable to boot up win7 installation

MacBook Pro Mid 2011

I was using boot camp all the long. today i decided to reformat my OS X and Boot Camp. so i clean installed my snow leopard then install boot camp.

As i completed the partition for bootcamp installation, i pressed install window and my MBP restart. Instead of booting up to window setup, my screen stuck right after the apple logo with black screen and a blinking _ at the top left corner.

I have been using the same method for the pass few times. Im not sure why it suddenly didnt work. regarded for reformatting when both my system working fine!

someone please help.