This is happening because the computer cannot successfully and fully load Windows. This is most likely caused by a faulty Windows Update or upgrade or software (driver) problem.
At first, I can suggest you try these 2 (depending on what has happened):
1. Please, shutdown the computer using the power button
2. Power it on.
2.1 As soon as you press the power-on button, immediately begin hitting the Esc button (like tap-tap-tap).
This should open a HP Startup Menu which may look similar to this one
3. Choose F11 for System Recovery options.
The computer should boot from it's recovery partition to open you various recovery options. Note, that F11 option will only work if the recovery partition is there (not deleted) and intact. From there, you have prenty of options to choose from. Every HP computer comes with recovery partition present to assist in tough moments.