TechWolf

so i downloaded 1.8 and it worked great, but i recently realized after downloading it now i cant open any of my other versions, i just downloaded the forge 1.7.10 for a different server but when i hit the play button and it downloads the nessisary files it just closes out and doesnt go further, i downloaded a mod that was suppost to fix the problem but it also didnt help, what am i doing wrong?