Quiet Life, Thanks for your suggestion to download Disc Wizard from seagate site which i did it.
But it is little confusing me because when i tried to add the disc, the wizard says the some partition is already made and it has to be formatted to make new partitions. The total space is 250gb but i am able to view just 232gb, i wonder where has the 18gb gone, when i opened the partition i could see just a seagate pdf file of 2.5mb or so.
A 250gb harddrive will only show as 232gb in Windows as it is calculated in a different way. You have not lost any space. Your existing internal drive will show the same percentage reduction in size. I do not know what the Seagate pdf file is but it is probably instructions re your new drive. Save it to your other drive for future or current reference and then format and partition the new drive.