hard disk problem or the enclosure problem?

i have an old 80 gb seagate ide hard disk which i use as external to my new machine.the problem is that i use it in a 3.5 ide hdd enclosure with usb 2.0.i am using this enclosure for the past two years,frequently whenever i used to plugin the hard disk to my pc,it used to freeze xp.but after reboot it used to run normally.now the problem is whenever i am coonecting it to the pc,it shows a new hardware is found and used to freeze xp until i restart it directly,and after restart,if i plugin the usb to the pc,the same thing happens.is it my hard disk is dying or is it the enclosure is having some problem,i changed the adapter cable,the usb cable,but nothing happens xcept the same thing.plz.help me out guyz.