IPhone 8 - the screen on my mobile has gone blank. I wonder what's the problem?

Added 3+ months ago:

My mobile is a Pay As You Go Sony Ericsson k800i. I thought there was something wrong with the battery, So I bought a second hand battery of the same make but the problem is the same, the screen light up and is blank. When I press the power-on button to power the phone, I can hear the buzz inside the phone but the screen stay blank. None of the key numbers light up either.