Hi

My old disk with data is showing the unallocated
When I right click on that in disk management it is not showing iniliaze option

Please tell me what I do...

Is there a "New Partition" option? If so then that's what you can do is to create a new partition on it. Or if what you want is to extend the size of your existing partition then you need a 3rd party package like PartitionMagic to extend the existing partition by the amount of unallocated space on that hard drive.