Vista won't recognise external hdd, works with xp!!?

The drive should be in my computer and other external drives I think. It could be that the driver is not compatible with Vista. Then you would need a new drive. This is more likely if it is an older drive. If you still have the box to the drive check to see it it is vista compatible. It could also be that your ports are not working (maybe they short circuited). In that case you need to bring it in to a tech store.