I wasn't doing anything special with the phone, but it was acting weird - didn't allow me to make calls, hang them up in the middle, and restarted the phone, until it didn't turn on again.
It's now completely black, connecting to charger doesn't do anything either.
I tried different batteries, didn't help.
After putting the battery in and trying to turn it on, even though nothing is visible - the phone gets warmer after few minutes.
I'm pretty sure it's not the screen because I would've hear the opening sound and feel the vibration..