Laptop won't turn on, even repair can't help

My laptop was working fine then one day it wouldn't turn on. I tried everything but there wasn't a single light blinking. Then it turned on for about a day. I turned it off and was the same as before for two days. Then it worked perfectly fine for two more days. And since yesterday it won't rurn on and the LED lights don't blink as well. I took it to repair but they said that there was nothing wrong with it - the guy from repair opened the core, checked the battery and charger and gave it to few of his colleagues but no one found anythinf wrong with it, so they returned it to me because there was nothing they could do. I tried removing the battery and unplugging the adapter, pressing the start button for 30/60 seconds - it doesn't work. Different chargers or sockets don't make a diffetence. Putting the charger without the battery does nothing. No lights, no sounds, no nothing. I tried leaving it unplugged and without battery for a whole night as well as charging it all nigt but there was no difference. Laaptop is cold to the touch, only the box on the adapter is warm.