The PC works fine when active, if for example I run a defrag or virus scan, no problems, it runs to completion.
However if I just leave the PC active with nothing running after about 20 minutes it goes to sleep, when this happens I hear some activity on the HD but that might be coincidental.
The power scheme is set off, therefore it is probably nothing to do with hibernation or sleep mode.
When I say it goes to sleep nothing unusual happens until I select sometning on the screen with the Mouse, eg. open a folder. Then I just get the egg-timer and nothing else .. Unless I reboot.
I have changed have flashed the BIOS just in case its an acpi problem, but that made no difference.