How to enable interrupt again after disabling it?
Below I am trying to disable interrupt once it got detected and enable it again when I start loop again. 


not sure why you want to do that but interrupts are DISABLED in isr by hardware (unless you explicitly enable it in isr) so what you are trying to do is done for you automagically.


  But in below code I am not able to enable it.


mostly it involves enabling the respective interrupt mask, unless you want to enable / disable all interrupts.