Hello,
By the looks of your post it only seems your Indian Ringneck has been with you for four weeks. Four weeks is not a lot of time for the bird to adjust to its surroundings and you. These creatures are naturally fearful due to the fact they are hunted in the wild by predators. In fact, Indian Ringneck's are sentinel parrots and will quickly alert their flock mates that danger is around by making loud shrill calls through a crescendo.
Let me put this in perspective for you. I purchased a pair of African Ringnecks and house them in my outside aviary. These birds were obviously caught and imported and are extremely fearful of humans. The moment I get close to their aviary compartment the pair begins to make sentinel calls. I have had them for roughly 2 years now and they are slowly adapting to my presence. Does this mean you're ringneck will take about two years to stop this behavior? The answer is no.
The good news is your Indian Ringneck is housed alone and is caged within the house. There are no other birds to influence his behavior and it seems from your post you are working with him. This constant interaction will quickly help him learn that you mean no harm.
Now, this leads me to the big question – to clip or not the clip? The answer is totally up to you as it tends to be a controversial subject to say the least. I personally would clip his wings while he's being trained and let them grow as he progresses. But, the decision is in your hands to make the choice. On a side note, I am experimenting with Archimedes and Devri with their wings grown out and I love it.
When you are training him you should start a positive reinforcement program and gradually work your way up.
So how can you minimize the screaming behavior. It's simple, pull up a chair next to him and read a book aloud and talk to him. Don't make direct eye contact and reward him with pieces of fruit or treats that he likes. Over time he will come to accept your presence and it will be no big deal when you're around. Remember, it takes time and every bird is different.
I hope this helps and please keep us updated.
Best wishes,
IMRAN-C
...... 
Now its only 4 weeks since he came to my house.So how can i change this behaviour? He has just started to talk what we taught him a little bit.But he still screams. He is alone in his cage and his cage is not so big.I did not clipp his wings.Is it neccesary to clipp his wings to spend more time with him? Actually we cannot take him out without clipping his wings.Is it necessary to take him out of the cage to change this screaming.Can u give the answers as soon as possible?I think these informations are enough for the answers..... 
. When we go near him for giving him food or something he starts screaming...........This makes me completely sad...... I think he is not getting used to us.As I mentioned above its 7 months since our parrot came to our house......So i dont know why he's screaming......He now says what we taught him.Actually he is in a cage ........ His wings r not clipped.......So how can I change his behaviour.....Should there be more time for him to get used to us? PLZZZZZZZZZZ REPLY!!!!!!!!! 
.....