Hello Forum, I'm using a Dell Dimension 5150 with a Hitachi and a Maxtor HD. The Hitachi (C drive) came with the machine with XP Home edition. I then added the Maxtor with XP Professional (D-drive). For a while, both drives were bootable, with the OS boot choice being given at startup. While in the D drive, I could always see the C drive and search it. A while later I found that the C (Hitachi with XP-Home) would not boot. I didn't much care because I had planned to use only my D drive and use C for backup. I may have set the RAID function on and off again - can't remember. Yesterday I detached the (perfectly working) Maxtor and installed XP Pro on the Hitachi C drive and it will boot but now... the Maxtor will not. While in C, the Maxtor is not seen in My Computer or in the defrag tool but it is seen in Device Manager and in Disk Management. Here it has the status 'Active' and the C drive has the status 'System'. I call it the 'D' drive but the Maxtor has no letter assigned to it. The "Change Letter and Drive Path" option (on the right click) in Disk Management is greyed out. In BIOS, one drive is labeled 0 and the other is labeled 1. Either the C, Hitachi drive will boot or, when I switch the data feed cables, I will get the message "No boot device available." Both drives are SATA, they are enabled in BIOS, they are NTSF formatted and the BIOS boot sequence is set for SATA HD. I'm not inclined to turn on RAID as I seem to remember reading that it can prevent the drive from booting (as of course is the problem already.) I entered a new computer name when installing XP Pro. The C drive Hitachi will only boot from one of the two data cables and only when the Maxtor is also connected. Alone, or with the wrong data cable I'll get the message "Drive 0 not found: Setial ATA, SATA-0." Any help at all would be absolutely appreciated.