How can I try to boot a completely stuck Macbook Pro? I have a retina MBP that according to my mum was working last time she put it under charge (with 15% left). However, as of now, I get no reaction at all after pressing the boot key. The screen stays off and I hear no noise. The computer has been under charge for several hours, but the charge indicator is not turning to green.

The laptop is under (European) warranty for the next few months. However, I'm reluctant in trying that route because I think it would be denied (at a charge) and I don't have file vault enabled.

Is there something I can try myself? I'm the kind of guy with a oscilloscope on his workbench.

Edit: The MBP started to work again out of the blue today without any action from my side. See my comment here.
It could be something as simple as the MagSafe DC board or it could be the whole logic board. See below:



Normally, I wouldn't recommend that a user change out this part as Apple goes out of their way to make a complex assembly, but since you have an oscilloscope on your workbench....

The part is relatively inexpensive as compared to a logic board and I have fixed MacBooks where this component has failed.  Ifixit has excellent tear down instructions on how to get at this component.

You didn't specify which specific model, so I grabbed the 2013 model for reference.  The link is:  https://www.ifixit.com/Guide/MacBook+Pro+15-Inch+Retina+Display+Early+2013+MagSafe+DC-In+Board+Replacement/17055.

If it isn't the right model, you can find the correct one on their site.  I hope this helps...