MacBook 12 2015 wont turn one

I’ve got a hand-me-down MacBook 12 2016 which shows no signs of life.

I was told it was taken in to apple store for repair some years ago for a memory problem. They took a few weeks to repair it, by which time the owner had replaced it, so the apparently-fixed macbook went straight on the shelf.

Fast forward to now, it wont switch on at all.

I’ve checked the (usb-c) charger on my phone, it charges that fine.

The first few hours I had it plugged in, the charger got a bit warm, now it stays cool to the touch though.

I’ve tried SMC reset; left hand shift, control, option keys and power, both with and without power cable plugged in, no change.

With the back off, I can see the little white led near the battery-disconnect button, on normally.

If I hold the battery-disconnect button, it goes off. Plug power back in, it comes back on.

After battery-disconnect button, pressing the power button does nothing, does not bring the light back on, only plugging in power cable does.

Watching the led, holding SMC reset key combination I see it flash every 5 seconds, so it seems the power switch does actually work.

Is there anything else I could try before taking it into an apple store?