What economic problems contributed to the collapse of the Umayyads?

The Umayyads had conquered many new lands and peoples for Islam, but in 750 AD, after 90 years of continuous rule, they faced some serious economic and political problems. If you were a non-Muslim, you had to pay a few more taxes than the Muslims. If you became a Muslim, you wouldn't have to pay those extra fees anymore. The majority of the non-Muslims said,"to hell with it" and became Muslims so they wouldn't have to pay. Consequently, as the number of conversions to the Islamic culture increased, the amount of tax money available for the empire decreased.