Guys, I had a problem after update and my system didn’t work, and I saw “cannot start the ps4” inscription every time. I tried to reinstall the firmware(number 7 in a safe mode), but it didn’t help and after firmware reinstalling my system show me Playstation logo and then the screen turned black..... but it seems like I found the solution. So, i have bought a brand new hdd some hours ago and changed the old one with the new one, because I thought that something bad happend with my hdd. AND IT WORKED! With my old hdd after reinstalling firmware ps didn’t work, but with the new one it works. I don’t know that happend after update, but new hdd saved me, maybe it will help you too ?
and also, please, try to not download update by internet, use your pc and usb, because it’s safer. Probably update file did something with me hdd.......
And also, you can try not to buy a new hdd, but connect your current to your pc and format it, and then try to use it with your PS4 maybe it will help.