Thanks Trepex
Well its working now, bit strange why.
It was a Icy box usb / firewire enclosure with a hitachi 500gb hd.
Looking in disk utility the device would be present but no hd. the device name was garbled and reporting a 2 tb drive? trying to erase or partition would respond in disk utility crash or a inout/output error.
Anyway put the hd in a old pc to format it in ntfs (cant remeber), put it back in enclosure and its all working fine, just formatted it into apple
To be honest not overly impressed with icy box, cables a bit on the short side