If you have a Windows 8 install disc or repair disc, boot from that and attempt the repair. If you don't have either, find another Windows 8 system and create one. You just go to Control Panel -> Backup and Restore -> Create a system repair disc (or flash drive).
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Good luck.
I'm not very tech savvy so please be simple. My computer won't boot when I attempt to boot it up it displays: "selected boot did not authenticate" and hitting enter only turns it off. I'm not sure how to fix this problem and any help would be appreciated, it is an HP laptop and has Windows 8 installed by default.

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