I just checked and your computer (your model) is not Windows 10 compatible. HP hasn't officially released Windows 10 drivers and Windows 10 is not officially supported on this model. The only officially supported Windows is Windows 7.
You need to use HP Recovery media that will reinstall Windows 7 and will restore your software, drivers, everything to factory default condition - just like the moment you purchased it.
Option 1) You can contact HP support to see if they can offer you original recovery media for this computer (a.k.a. recovery DVDs or USB).
Once ready, please, shutdown the computer using the power button.
Insert the Windows USB thumdrive prepared previously
Power on the PC.
As soon as you press the power-on button, keep hitting the Esc button (like tap-tap-tap).
This should open a HP Startup Menu which may look similar to this one
Choose F9 to open Boot options. Select the thumb drive or DVDs as boot option.
Follow the on-screen instructions to install Windows
Please, let me know if this works for you. Do not hesitate to post again if something is not clear.
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