Check graphics card fan is working and that graphics card is seated properly. Unplug and then plug graphics card back in. Do you get the usual BIOS messages etc on power up. If not, then unlikely to be hard disc.
Graphics card fan is working.Have unplugged card and reinserted it. No BIOS messages on screen at power up. Not sure if my imagination butI thought I detected a barely audible high pitched whine when computer was switched off but with power on.
Iscanut - I have come to the same conclusion. It would appear from previous postings that this is not a HDD problem although it would have been comforting to see the HDD light flickering as if it was loading; howver, realise that PSU delivery or motherboard could cause the problem.