Computer was turned on when going to sleep, in the morning it was off. Now it won't turn on. Age ~1 year.
When holding the power button a very dim buzzing noise can be heard when keeping an ear close to the keyboard. When I release the button, the on/off LED blinks for a second, but only if the battery is connected. With charger and without battery it won't work. The light for the charger won't turn on when charger is connected. Charger itself is totally okay, not older than a month and outputs 19.4V as it should. That current also makes it to the mb just fine.
Already tried all the 'normal' measures like remove battery, replug, remove HDD, replug etc.

Since you've try the 'normal' measures to fix it, why not doing it again but this time just let it unplug from any battery/charger for a day.

If this not working, then most probably you have a dead laptop already. I doubt changing RAM and even HDD would do anything to fix it.