Problem booting from win7 usb

Hello,
I'm trying to install windows 7 on my 15" mbp running OSX lion.
It's a end 2011 series.
I have a working bootable USB created with the "windows 7 usb dvd tool"
I'm pretty sure it works because i'm able to boot from it on my windows xp pc.
Using bootcamp, i made a 75Gb windows partition,
but wen the mbp restarts after making the partition i only get a black screen saying
"no bootable device insert boot disk and press any key"
I've tried taking the usb out, and putting it back in, no succes.
I've hit every key on my keyboard, no succes.
Also, I can't use the usb as a start up disk, because it isn't in the list (in the preferance panel)
I hope someone can help me with my problem.
Funny how the only trouble i've had with mac in 8 years, is installing windows.
btw I'm new to mac-forums, so if i posted this in the wrong tread, i apologize
Thanks,
Louis

Are you trying to boot Windows 7 from a USB drive? Booting Windows off an external drive is not supported on Macs. This article elaborates on this a bit, with possible UNSUPPORTED workarounds:
AppleInsider | Exploring Windows 7 on the Mac: installation via Boot Camp

Please excuse my addressing an old thread, but it is possible to make a bootable USB drive for the installation of windows, even for machines that don't initially support this feature (when using bootcamp 4.0 or later and a tweak). The issue with your install may be that the partition itself did not complete the process, or that you have other peripheral devices connected to the machine.
In any event, it may be beneficial to you (or anyone else it may concern) to restart the installation process and install windows from start to end in a single session. I had issues with my install when I chose to install it later, doing so from USB in a single process was problem free. Hope this helps for you and whomever else it may concern.