Hi Shahul,
There is either a connection problem or you code is not properly reading the value. A shorted input should be near 0 code and not full-scale. The best way to isolate code issues is to look at the output data as it is being read out of the device. Place an oscilloscope probe on SCLK and another on DOUT/DRDY and see if the code you interpret from the scope is the same as your processor output.
Did you read my previous comments on your design in this posting?
http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/279453.aspx
Best regards,
Bob B