I would recommend the following:
Show personal interest. If it's really important to you, then it's worth a phone call, a visit, or something else that makes that fact self-evident. A lot of urgency and importance can be politely communicated by a show of personal dedication.
Give the benefit of the doubt. Often when my superiors haven't responded to my email it's because they're busy and haven't gotten to it yet. Usually they have received the email and already have a solution in mind. Approach the recipient of your email with a smile, be friendly, and ask them if they saw your message. Chances are they have and they can talk to you about it.
Explain the importance of the situation. If the situation really is urgent, calmly give the recipient important details that they might not know yet so they can effectively prioritize and implement their solution. If they decide it's not a high priority and they assume responsibility for it, then don't worry about it.
Be patient. If you aren't getting the results you want, find something else productive to do. There are always opportunities available. Take advantage of the time you have to make a difference. Doing the right thing in times of difficulty will set you apart from other employees and prepare you for future problems.