Once the English had bought Joan from the Burgundians, she was convicted of witcchcraft and sentenced to death. In 1431 she was burned at the stake in Rouen, France.
After Joan was killed, Philip the good switched sides to help the French in 1435.
After Philip switched sides, England had internal struggles which made it harder to fight the battles. While the English were having trouble the French took that as an opportunity to drive them out while they were weak. They succeeded in this and won the war, also the weapons they were using were also very advanced this helped them to defeat England.