XPS Studio 8100 - External Esata Problem

Having a small problem with the rear external esata socket.

Windows 7 does not autodetect a HDD when plugged in to the external esata socket - I can force windows 7(x64 professional) to see the HDD by doing a 'hardware scan for changes' each time I connect it, which is ok - but its a pain!

Vista used to pick a change up automatically!

Is there an obscure setting somewhere?

I have read something about an AHCI driver and a bios setting required but not had any luck finding a specific solution

Hope you guys can help

Garry