well small update, have been given an hd 6870 to try instead of the gtx 460 which is working fine in an old pc now, but im still getting the same problem but less frequently, yet scince then i have noticed my 12v is sitting really low at 10.8v could this be a hint that a new psu is in order?
It COULD be, read the post above you, can you borrow a PSU to test?