My laptop is charging yet not switching on

It sounds likely that you need to replace the battery; the behavior you describe matches the symptoms of a battery that can no longer hold a charge. Even though it may say it's fully charged, it's likely there isn't enough charge in it to power the laptop. Imagine a jar representing a battery. You fill the jar with water (charge the battery), but every time you do, you add a marble to the jar. Over time, the space inside the jar gets filled with marbles and can't hold as much water as a result. Eventually the jar is full of marbles, and even though you fill the jar with water clear to the top, the amount of water in the jar is only a fraction of what it originally held when it was empty.

Your battery works the same way; eventually the chemical reactions that generate power break down until it gets to the point where there is so little power available that it can't run your computer.

So I'd say your best bet is to start with replacing the battery, then reevaluate whether it's working correctly or not. We would need the model number from the bottom label of your laptop in order to look up instructions on how you can do that, so if you can edit your question or add a comment with that information, we should be able to find you a guide.

You could try HP's recommended procedure for checking the battery, but note that one of the steps is to unplug the laptop, which won't work in your case so I'd suggest skipping that step and see if it works anyway.

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