It sometimes days the game is modded,but now it doesnt,and i think it stopped working when i updated to windows 10

Put the summary of the bug you're having here

What I expected to happen was...:
I push the play button and minecraft starts at the menu screen

What actually happened was...:
It brings up an error message

Steps to Reproduce:
1.I open the minecraft launcher
2.I click the play button
3.And then it brings up the error message