PS4 stuck in Safe Mode, can't update it via USB

Title, basically. My brother gave me his PS4 to fix, but it’s stuck in this Safe Mode where it wants me to update it with a USB. I’ve gone to the PlayStation website itself, downloaded the update, that didn’t work, I went to a different website (DarkSoftware), tried the same thing, didn’t work. Tried different versions of the update (as in, 7.50, 9.00, etc.) didn’t work. And I’m doing everything correctly as far as I know, the USB is Fat32, the folders are on there, but, still, no luck. I don’t think there were any problems prior (not that I know of), so I don’t get it. I’ve gotten two different error messages; one where it says the USB isn’t connected when it is (that’s usually when I use the PUP file from Playstation’s website) and one where it says the update file cannot be used. Really, man, anything helps. Thanks in advance!