Chosen Solution
Hi, everyone! I was using my MBP 2010 booting from an external drive cause the HDD cable was broken, then two days ago I replaced the cable and now it doesn’t boot. Everything makes noise running, but after 5sec the MPB turn off and then turn on again and continuing until I press SHIFT+CTRL+OPTION+POWER to turn it off. I made a record: https://youtu.be/iocJlE1y-go Can anyone help me, please?
At this point lets unplug the HD cable from the drive and see what it does. Do you here the Bong and get a flashing question mark on the folder on the screen? Reference: About the screens you see when your Mac starts up
