Computer repair

Hello,
1. Was just trying to change my laptop windows from windows 8 to windows 7 and after booting from ROM/DVD ROM the set up was copied and it gave me information that it will restart and instead of restarting a blue screen appeared with a message stating that " the windows has shut down to prevent break down. what is the problem? Kindly assist?

2. All the USB ports on my laptop doesn't sense flash-disc or any USB material. Assist please