Question

The colonists did not win the battle at fort Duq uesne in 1755 what cuased this

Answer 1

There were a number of reasons for the defeat of the British troops in the battle at Fort Duquesne (or Battle of the Monongahela). The expedition it was part of started badly, and due to to narrow roads, the British forces needed to split in two, with the soldiers who could move faster in front, and the others in the back along with canons.
The British did in fact surprise their opponents, but the quick response of the French has given the impression of their great force. The British had a psychological disadvantage, and their actions were unorganized and unproductive, and at times they even attacked each other in confusion.
The final blow was the commander of the British troops, Braddock, being shot and wounded in the lung: after his falling from the horse, the British troops withdrew, and panic followed.

Note: the battle was between British troops and an alliance of French, Canadian and Native American troops, and the French are also colonists, so colonist (different ones) both won and lost the battle.