We got a brand new PC 4 weeks ago with two physical HDDs (160GB each). C: for XP and D: for Vista

All worked OK for 2 weeks and now occasionally the drive D: can not be found and as a result Vista can not boot.

After unplugging the PC from the mains the Drive D: does 'sometimes' show up again in XP but when re-booting in Vista (now very slow) we get error that some services clients can not load (LAN and others) - hence don't work.

When I had a look at the hardware I found that one HDD (C:) is connected to the power supply with a cable marked SATA (yellow, 2xblack, red, orange) but the other drive (D: same model) is only connected to a regular loop-through cable with the fans (yellow, 2xblack, red).

Could this have any significance?

In XP everything is working OK apart from the fact the drive D: is sometimes not available.

Is this a hardware or software problem?

opalhort

A more apt title would be "disappearing HD problem". Seems obvious to me that it's a hardware problem. Could be that cable, or the HD is simply going out. Make sure that all cables in the HD are plugged in properly and if that doesn't help - you could try and replace the power cable or take it to the shop under warranty. I would do the latter since it's only 4 weeks old...