If i have a mental disorder which makes me go violent, will i get away with a murder?

No, you won't get away with anything because you're already imprisoned in and by your own mind. Will you be in trouble? Yes. Can you be held responsible? Maybe not... but there are cases where very mentally troubled people were held accountable for their actions because they knew the difference between right and wrong. Not every mentally ill person gets away with murder. Mental illness is not an automatic "Get Out Of Jail Free" card.