Hi Piet1954,

If I understand correctly, the drive is present in the BIOS but absent in Windows? Both Explorer and device manager? What if you boot to safe mode?

Good suggestion: in safe mode the hdd (volumes F: and G:) were back again. And after normal start-up this still is the case.

Do you have a clue what might cause the trouble?

And/or do you have suggestions on how to watch the system in order to find out what is actually happening when the hdd/volumes disappear again after some time?

Thanks for your help!

What's the operating system?

Does this happen after resuming from sleep or hibernate? 

Windows XP SP3

When...? That actually is the question.

I never set the system in hibernate. Also all energy-saving settings (sleepmode, standby, hdd-off) are off, except screensaving.

The hdd/volumes are still alive, now.

Any suggestions like some system guarding tool that notices a hdd when it's gone?

No, but I actually don't work on this drive on a daily basis. It has a great transfer rate, so I now and then use it for video-editing and always backup externally.

Thanks for your assistance so far. I might be back when these problems pop up again.

It's pretty strange all right. I think you're smart to keep an eye on it. I believe the current version of the Dell support tool has a monitoring tool that might be useful.