Molex 5volt low and unstable?

Hi, my goodmans 80 gig HDD set top box suddenly stopped working. It's completely dead. I've removed the Samsung HDD and connected it up to my computer and though it wont let me access the files it seems ok(you can hear it working and you can see it via linux)
I've tested the molex supply to the HDD and the 12volt is spot on but the 5volt stays below 1volt and fluctuates.
Can anyone please advise.
Thankyou