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At the first press of the power button to switch on the computer, the hard disk is not detected, BIOS says "unknown device" instead of hard disk. Then I switch off the computer by pressing the power button and turn it back on and then as if by magic, the hard-disk is detected and everything boots up and works fine.

I am forced to think that the hard-drive is bad, (I did change the hard drive cable with a new one but with no success).

This has been happening for a week and without fail, it always works the second time the computer is switched on. The switching on-off-on must occur one after the other with no or a few seconds time interval.

Why does it always work the second time?

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up vote 4 down vote accepted

Sometimes this is caused by the computer trying to boot before the harddrive has time to spin up. I believe this usually happens on drives which have many platters (due to the weight the motor takes longer to get up to speed), but that may be entirely incorrect ;-)

Usually there's a setting in the bios to add a delay before detecting the disks. I'd suggest trying there first.

edit: this article indicates it's actually due to ide drives taking longer to initialise. Same solution, though.

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thanks will try and get back – Doopy Doo Feb 9 '12 at 14:54

Check the bios for a quick boot (or similar) setting, turn it off, it should allow a more thorough hardware check when turned off, see if this gives the drive more time to spin up and stop giving you this error.

I agree, your hard drive may be dying a slow death of the spindle motor or bearings, back up your data and replace it.

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