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As I understand the computer is powering on but there's no display on the screen, The computer turns off after a few seconds after it's turned on,
To provide an accurate solution, I'll need a few more details:
What is the product number of this computer? (Ensure you do not share any of your personal information such as serial, phone number, email ID, etc...).
Have you performed any steps on your own before posting on the HP Forums?
In the meantime, you perform the below steps:
Let's start off by performing a Hard reset on the notebook: A power reset (or hard restart) clears all information from the computer's memory without erasing any personal data. Performing a power reset might fix conditions such as Windows not responding, a blank display, software freezing, the keyboard stops responding, or other external devices locking up.
If the computer still turns off every few seconds, try with an alternate adapter and/or remove the battery and try turning on the computer without the battery, only connect the adapter and start, let me know if that works.