In the same year, the city fell victim to a great fire, which burned 350 buildings, two churches and the Nassau Court, the headquarters of the ruling family.

His father had remarried with Isabella Clara du Puget de la Serre and had had seven surviving children with her.

William Hyacinth traveled to Paris to secure the support of France with regard to his rights of inheritance.

Louis XIV declared that the Prince Henri Jules of Condé was the rightful heir to the principality of Orange and occupied it militarily.

His lavish court, with which he wanted to underscore his claim to the inheritance of Orange, his journeys and gifts cost far more than his income from the Duchy of Nassau-Siegen could bear.

William Hyacinth was consequently indebted to the bankers De Rhön and Schonemann from Frankfurt, pledging of the villages Wilnsdorf and Wilgersdorf for 20000talers.

When William Hyacinth visited the court in Vienna in 1705, to raise support for his inheritance claim, Siegen was occupied by troops from Nassau and Prussia.

On 15 July 1706, Siegen was again occupied, this time by troops from County Palatine of Neuburg and Prussia, at the request of the Aulic Council.

On 29 March 1707 William Hyacinth had Friedrich Flender von der Hardt, a suspected leader of the insurgents, beheaded without any form of trial.

The remaining assets were used to pay the pensions of his stepmother and her siblings, his creditors and a debt of honor to the family of Friedrich Flender.