I assume you've solved the problem, but for future use, when the boot screen fires up on an HP DV6 laptop pressing F9 (usually, it may be different on yours) brings up the boot options (usb, external hard drive, local drive, and so on - whatever you have connected to your laptop that the bios recognises). After pressing F9 you should see a menu, select the option linked to the media you wish to boot off. I notice this is the only way I can get my Win7 desktop to boot into Knoppix from a USB or external drive too.
Hope this helps you, or someone who reads this...