HOWEVER... you should be able to press the "pilot" button and get it to fire. When powering up the flash, the pilot may be green (meaning it's on, but not yet ready to fire) and should go red when ready to fire. Does it go red for you (meaning the batteries were able to charge up the capacitors)? I think the flash should _always_ fire for you as long as it's "on" and the pilot lamp is "red" (not green... green is NOT ready to fire. Why Canon used "green" for on, but not ready and "red" for ready... I think is just confusing. Most people would intuitively think of a "green" light as meaning you're good to go.
You may have a lemon, but in the case of the 430EX II that is exceptionally rare... this flash is typically one of the more solid performers (the 580EX II -- technically a bit more "pro" and higher power -- actually has a higher failure rate than the 430EX II.)