Try Power drain(Remove all power source and press the power button for few seconds.)
If you are able to boot to BIOS, try doing BIOS default. F10 leads to BIOS.
If you are able to boot to safe mdoe, first thing first mate, do a Graphics driver upgrade and also can do BIOS, Chipset, other related drivers, upgrade, or all the drivers can be updated to the latest available once.
If unabe to boot at all.
Try Refixing the Graphic cards, RAM and Cmos and connector(please refer to HP SML(google it) for How to remove and refix hardwares.)
Keep posting the update.
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