External HD freezes XP-computer but not W7

Hello,
Experiencing a strange problem. External HD (WD 1TB - 2 partitions 450GB each) always worked perfectly on computers with XP. When I plug in the HD now in (any) XP-computer, the computer freezes and satys that way even after pulling the USB-plug from the computer. Using the computer again is only possible by a forced restart because the computer does not respond to anything.
Weird is that: 1) the external HD has worked fine on XP-machines before until recently (perhaps a XP-update is the cause?); 2) the HD works perfectly on a W7 computer.
Who has any idea? For the record: partition is active, cables checked, tried several XP machines (which all respond to the HD in the same way), nothing wrong with the USB-ports, etc.