Thanks NAIC, tried that a few times, but chkdsk won't run under any circs - conclusion - duff hdd.
Actually running ok now, but I'm leery of turning it off at the mo due to the boot up instability I get each time. In the medium term it'll create probs cos' defrag won't run until check disk has run & check disk won't run full stop, so I'll end up with a slower & slower machine as files get fragmented over time - answer - new HDD, and it's still under warranty
