I bought a Samsung HD501LJ Harddrive which i connected up and installed under Vista64 and added all important data to the disk. After reinstalling XP home the drive is not visible or accessible. It appears under Hardware Profiles but i cant change or alter any settings even under Disk Manager. I have reinstalled Vista and can now access the Drive and the data - how can i make the drive accessible under XP as i need to revert back

Is the Vista 64 drive a SATA drive? Is the Winxp drive a SATA drive? Have you looked in Disk managment when you are in WinXP? If the drive shows there you need to take ownership of the files. Look below to find out how. http://support.microsoft.com/kb/308421

What im trying to do is revert back to XP, when i install XP (removing Vista64 and installing XP over that drive) i cannot access my secondary harddrive. The problem i have is that the drive is detected but its it is not visible at all under My Computer. Its only has the local drive (C:) but doesn't have the second drive at all - as if XP doesn't undertand what the drive is, so doesn't display it

As I said look in Disk Management. Right click My computer> manage> storage> disk management. You may need to take ownership of the disk/files.

Ok, i have reinstalled Vista so tomorrow i will install XP again and see if this works. I'll report back - if anyone knows of anything else i can try it will be very much appreciated. Thank you

Was the hdd partitioned with Vista or XP ? Vista can partition a hdd that XP can not understand at all. May have to get into XP's recovery console and run 'diskpart' and see what it says for the partition or any third party program that will display the Master Partition Table. Edit: could not find the MS article I was looking for but this one could be the paroblem: http://support.microsoft.com/kb/931...