Similar problems on a few machines. The first had a failing HDD, the next required I delete all the partitions on the HDD then start the W10 install again and tell it to use the now blank, no partition, unformatted HDD.
Both are fixed now.
I have a Toshiba Satellite P55W-C5314 I just bought a couple months ago. It had been occasionally (maybe once every day or two), for no reason, restarting on its own while I was in the middle of using it. I just attempted to reload Windows 10 with a thumb drive of it sent with it by the eBay seller (who refused to reply to my multiple messages regarding this defect) to me in hopes it would fix the problem. It now just loops from the 'Hi there' screen where you input country, app language, keyboard layout and time zone to 'Let's get connected' where you choose your wifi connection to 'Get going fast' where I've chosen both the Express Settings and Customize Settings options to the blue screen 'Just a moment...' where it blinks off once and back to the blue screen for another moment, then to Toshiba Leading Innovation >>>, blinks off and back to Toshiba Leading Innovation >>>, then to the 'Hi there' screen to begin anew. Please excuse the in-depth detail, but I wanted to be comprehensive in the description. To bypass the looping I wanted to start it in 'safe mode.' In my attempts to do just that, I hit the f12 button when starting up to arrive at the Boot Menu. I entered <Enter Setup>. There was nothing there to help. I've found in other forums that to enter safe mode with my PC you need to start it up while hitting the f8 button. That doesn't work. It just boots right up to 'Hi there.' So, I'd appreciate any help on how I can in fact get to where I can boot up in safe mode or any other method that will get me out of this perpetual loop. Thanks.

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