If anybody tells you to cut your hair, DO NOT LISTEN -- unless you WANT to cut your hair. You can have longer hair or blonde hair (or both!) and still look professional. Wearing it up in a French twist kind of deal (not using those ugly claw clips -- doing it the real way) might be an idea. I don't know if you wear contacts or glasses, but I just read something about how people STILL tend to think you're smart/professional if you're wearing glasses, so a hot pair of frames might be good. I don't get it, but it might work.
Other than that, I say don't worry about it too much. Just wow people with your competence and professionalism, and you should be fine.
