From what you have said it is highly likely your fan has failed. It is a 2 to 3 hour job the first time.
Having looked at your how to's you will have no trouble completing this task. It is just nuts and bolts
If you get yourself a fan before the next international nano meet I will guide you through it and do it with you. ( assuming your there )
Best/easiest way forward is a two speed with a resistor, plug and play, however, I have also fitted the kenlowe kit for members, it's a little more work but again you will not have a problem.