now a days my 1 year old sony combo drive is respond in a strange way that is when i press button to
eject ( open) it sounds like dush dush ( means it tries to open with his sound but it cant) and not open.
in 2 or 3 try it will open slowly .

i want to know the reason behind it

Try cleaning the drive with a cleaning kit.
When you try to eject your cd, do you see the access light blinking or is the drive not in reading mode