My Hanns G 28 is a piece of Chinesse $#1t. When there is no activity it goes off (by itself) and takes 24 hrs to turn on. Once it is on, it flickers for an hour after it warms up.
I have a smaller dell 21 inch that never gives trouble. The problem is the amazing quality of chinesse technology. i am pretty sure the middle guy paid $35.00 for the 28" and sold it to us for $200.00.
if you still have warranty, exchange it and expect new problems. Otherwise do a favor to society, TRASH IT and take your lost.