If a known-good replacement screen has the same symptoms, then your problem is on the logic board. The most likely culprit is the Chestnut IC (U3703). It drives the voltages which power the LCD. Interestingly, it also powers the Touch circuit but there could be a partial failure.
Now, because you ordered this phone on Amazon, you really don't know the history of the device. Was it tossed around, run over by a car ;>) or came into contact with water...who knows. So you or someone qualified will have to start probing this logic board to get a better understanding of what's wrong. If there was water damage, all bets are off.
Thanks @refectio , I forgot to mention that the phone is a certified refurbished not a used one. There is no trace of water because i've checked the board. When powered on, it just showed that faint backlight and the touchscreen responds when operated.
What did you suggest I should do to the Chestnut IC (U3703)? Should I re-heat or what.