Seperate hdd and os problem

I have xp32bit installed on my old hdd and recently installed windows 7 on a new hdd.
the new drive running windows 7 is working fine but when I switch drives in the bios to my old drive with xp I get to my desktop and shutdown due to a recent hardware change.
I discovered that unplugging my dvd rom power lead cures the problem.
Is this a sata port and or jumper problem?
sata 1 new hdd with windows 7 seperate power cable
sata 3 dvd rom shared power cable with sata 4
sata 4 old hdd with xp shared power cable
sata 2 runs to external port
would appreciate any help I can get......................