First, copy all your world files somewhere safe then delete your .minecraft folder and delete your minecraft launcher(you don't need to do so but just in case anything happens) go to the minecraft site download the launcher login like always then after it finishes downloading the files and play Hope This Helped!
found a fix I had to empty my hard drive and uninstall many programs from my control panel THEN allocate some ram my java and graphic card where both up to date so still thank you NuclearManx
I just have one more thing each time I play minecraft after 30 mins it starts to black out then gives me a error message closes minecraft then gives me black lines that make me restart my computer 3 times please help!!!
I would donate 6 million to the charity donate 6 million to mojang cause they made minecraft and give poor people so much money though all that money is not easy to achieve its like mission impossible and with great things or so much money comes great responsibility I WILL DONATE TO THE CHARITY AS MUCH AS I CAN!!