Power windows are also known as electric windows- that can be lowered and raised without any crank handle. A motorist can control the windows even while driving. Thus, the failure of power window regulator can be annoying. The failure of power window regulator not only will affect the up/down mechanism but will also affect the speed of up/down action. So, spotting the cause of failure is extremely crucial. Since the cause can be anything like a detached cable or a broken motor, hence I must say you should consult a reputable Audi specialist both for diagnosis and repair.