Minecraft java launcher wont open

i was chosing my skin in the launcher and then i went to options and i saw switch back to old launcher or something i can remember and i tought hmm lets see what the old launcher looked like and then i cliked it and it said that i needed to open the launcher again so i did but it was not opening so i tried to repair the minecraft launcher app but it didnt work so i tried to download Minecraft Java again but the same thing happend. any help?